We compared groups of opioid users new to methadone maintenance to determine if persons who first learn that they are HIV-seropositive in a drug treatment program are more likely to drop out of treatment than persons who learn they are seronegative. We found no difference in patients' continuation in methadone treatment at either 6 or 12 weeks associated with HIV serostatus. Our findings suggest that voluntary HIV testing can be implemented as part of AIDS prevention programs with little fear of adversely affecting treatment outcomes.