The extent to which interim methadone (IM) without counseling reduces HIV risk behavior has not been reported. The AIDS Risk Assessment scale was administered at baseline and 4-month follow-up to 319 adult heroin-dependent participants randomly assigned to IM or waiting list. On an intent-to-treat basis, there was a significantly greater reduction in drug injection and unprotected sex while high from baseline to follow-up, favoring the IM condition. Remedying the shortage of methadone capacity through the expansion of IM would be a worthwhile approach to reducing the spread of HIV infection.