A 12-week, randomized, double-blind, parallel-group, placebo-controlled trial of naltrexone will be conducted in 50 English- or Spanish-speaking outpatients with bipolar I disorder or II disorder and current alcohol dependence. At the baseline appointment, informed consent will be obtained, and assessment procedures, including a review of inclusion and exclusion criteria, will be performed. The SCID (Structured Clinical Interview for DMS-IV Axis I Disorders will be performed to establish the diagnoses of bipolar I or II disorder and alcohol dependence. A psychiatrist will confirm the SCID diagnoses obtained by the RA. Eligible participants will then be given the Hamilton Rating Scale for Depression 17-item version (HRSD17), Inventory of Depressive Symptomatology-Self-Report 30-item version (IDS-SR30), Young Mania Rating Scale (YMRS), Penn Alcohol Craving Scale (PACS), Addiction Severity Index (ASI), Psychobiology of Recovery in Depression III Somatic Symptom Scale (PRD-III), and a urine drug screen. Recent alcohol use (and if present other substance use) will be assessed using the Timeline Followback (TLFB) method, with a drink defined as 13.6g of absolute alcohol (approximately 12 oz (341 mL) of beer, 5 oz of wine, 3 oz of fortified wine, or 1.5 oz of 80 proof liquor). Length of problem alcohol use will be assessed by asking, "When did alcohol first start causing you problems?" Blood will be drawn for routine laboratory analyses including a complete blood count (CBC) and SMA-20 (includes a liver panel with GGT, AST, ALT, Billirubin) at baseline (week 0) and completion (week 12). Blood will also be drawn at weeks 4 and 8 for repeat testing of GGT levels. A physical examination will be performed at baseline. Women of childbearing potential will receive a urine pregnancy test and will be counseled about effective contraceptive methods. A psychiatrist will assess the participants at baseline and weekly follow-up visits, and will participate in the informed consent process. Study medication will be given at a second appointment after results of the liver function tests have been received (generally 1-2 days after the first appointment). At each weekly assessment the HRSD17, IDS-R30, YMRS, an assessment of alcohol use in the past week, and a urine drug screen will again be obtained. Urine drug screen will be obtained only from the newly enrolled subjects. We will not obtain urine drug screens from subjects who are already active in the study. In addition, all participants will receive a total of 16 one-hour/week sessions of manual-driven CBT specifically designed for persons with bipolar disorder and substance abuse, provided by a bilingual psychologist with experience in CBT. Patients will discontinue study medication at week 12, but continue their CBT therapy until week 16. Pill counts will be conducted at each weekly assessment visit. In addition, during weekly assessments, participants will be asked about adherence with other psychotropic medications using a modified version of an assessment developed by Weiss et al., and the estimated percent of prescribed medication actually taken will be recorded.