The patient population will consist of sexually active male and female patients, 18 years or older with a primary diagnosis of MDD, for whom the treating clinician makes a decision to treat with a SSRI or SNRI antidepressant. Eligible patients must agree to participate in the collection of data, and must not present with treatment resistant depression or have sexual dysfunction at study entry.

Inclusion Criteria:

• Meet the criteria for MDD, as defined by the ICD-10 or DSM-IV-TR
• Are at least moderately depressed (baseline CGI-S less than or equal to 4)
• Provide written consent to the release of their data after being informed about the study
• Present with an episode of MDD (current, new or first episode) within the normal course of care, and agree to initiate antidepressant therapy with any available SSRI or SNRI class of antidepressant in accordance with the investigator's decision for the management of the patient
• Have been sexually active in the week prior to enrollment, either with a partner or autoerotic activity

Exclusion Criteria:

• Meet any of the following criteria for sexual dysfunction at study entry (McGahuey et all. 2000: ASEX total score less than or equal 19 or ASEX score less than or equal to 5 on any item, or ASEX score less than or equal to 4 on any 3 items
• Are simultaneously participating in a different study that includes a treatment intervention and/or an investigational drug
• Have a history of treatment resistant depression (TRD) defined as a failure to respond to 2 different antidepressants from different classes after treatment at therapeutic dose for a minimum of 4 weeks
• Have any previous or current diagnosis of schizophrenia, schizophreniform, or schizoaffective disorder, bipolar disorder, dysthymia, mental retardation, or dementia
• Have received any antidepressant within 1 week prior to enrollment (1 month prior to enrollment for fluoxetine)