This article reports on the association between frequency of HIV testing and high-risk behaviors among 339 individuals in the Los Angeles Enhanced Methadone Maintenance Project. Individuals who reported taking three or more HIV tests prior to entering treatment (45% of the sample) were more likely to know someone who was HIV positive, to engage in illegal activity, to perceive their risk for HIV as high, and to use condoms; they were less likely to disinfect injection equipment; and they scored higher on measures of HIV knowledge and depression as compared with less frequent testers. The strongest predictor of frequent HIV testing (three or more tests) after treatment entry, reported by 43% of the sample, was having a high number of injection-sharing partners. Although a substantial number of individuals in methadone maintenance treatment continued to take HIV tests, test taking was more strongly related to high-risk injection behavior than to sexual behavior.