Inclusion Criteria:

• Provision of written informed consent before initiation of any study related procedures. Patients who are deemed incapable of providing informed consent maybe enrolled if written informed consent has been obtained from the patient's Legally Authorized Representative.
• Documented clinical diagnosis meeting the DSM-IV criteria for any of the following:
• 296.4X Bipolar Disorder I, Most Recent Episode Manic
• 296.0X Bipolar I Disorder, Single Manic Episode
• Have a YMRS score of at least 20 and a score of at least 4 on 2 of the following 4 YMRS items both at enrolment and at randomisation: Irritability, Speech, Content, and Disruptive/Aggressive Behaviour.
• Female patients of childbearing potential must have a negative urine pregnancy test at enrolment and be willing to use a reliable method of birth control, i.e., barrier method, oral contraceptive, implant, dermal contraception, long-term injectable contraceptive, intrauterine device, or tubal ligation, during the study.
• Be able to understand and comply with the requirements of the study, as judged by the investigator.

Exclusion Criteria:

• Manic episode judged to be either:
• the direct physiological consequence of a treatment or medical condition other than Bipolar disorder.
• the direct physiological effect of a substance of abuse; intoxication with hallucinogens, inhalants, opioids, or phencyclidine and related substances.
• the direct physiological effect of psychostimulant or antidepressant medication.
• Evidence of clinically severe or active disease, or a clinical finding that is unstable or that, in the opinion of the investigator, would be negatively affected by the study medication or that would affect the study medication.
• History of seizure disorder, except febrile convulsions.
• Hospitalization period of 3 weeks or longer immediately prior to randomization for the index manic episode.
• Known history of intolerance or hypersensitivity to quetiapine or lithium, or to any other component in the tablets/capsules.
• Known lack of response to quetiapine or lithium, as judged by the investigator.
• Use of antipsychotic medication or mood stabilizer other than quetiapine and lithium at the day of randomisation (to be tapered to discontinuation between the enrolment visit and randomisation).
• Administration of a depot antipsychotic injection within 1 dosing interval (for the depot) before randomisation.
• Use of clozapine within 28 days prior to randomisation.
• Use of antidepressants during the enrolment period or within a period of 5 half-lives of the drug(s) prior to randomisation.
• Continuous daily use of benzodiazepines in excess of 4 mg per day of lorazepam, or the equivalent, during 28 days prior to randomisation.
• Use of drugs that induce or inhibit the hepatic metabolizing cytochrome 3A4 enzymes within 14 days before randomisation.
• Receipt of electroconvulsive therapy (ECT) within 28 days prior to randomisation.
• Clinically significant deviation from the reference range in clinical laboratory test results at enrolment, as judged by the investigator.
• An absolute neutrophil count (ANC) of <1.5´109/L.
• Treatment with quetiapine with a dosage of at least 50 mg/day at enrolment (Visit 1)
• Liver function test AST or ALT 2 times as the upper normal limit.
• A thyroid-stimulating hormone (TSH) concentration more than 10% above the upper limit of the normal range of the laboratory used for sample analysis at enrolment, whether or not the subject is being treated for hypothyroidism.
• Known diagnosis of Diabetes Mellitus (DM) or fasting blood glucose level > the upper normal limit.
• Risk of transmitting human immuno-deficiency virus (HIV) or hepatitis B via blood or other body fluids, as judged by the investigator.
• ECG results considered to be clinically significant as determined by the investigator.
• Conditions that could affect absorption and metabolism of study medication.
• Patients who in the investigators opinion will require systematic psychotherapy (other than supportive psychotherapy) during the study period.
• Participation in another clinical study or compassionate use programme within 28 days prior to randomisation, or longer if locally required.
• Involvement in the planning and conduct of the study (applies to all AstraZeneca or staff at the investigational site).
• Previous enrolment or randomisation of treatment in the present study.