The close link between alcohol and other drug abuse and STD morbidity and the positive impact of AOD intervention services in reducing STD morbidity, led the New York State Office of Alcoholism and Substance Abuse Services (OASAS) and the New York City Bureau of STD Control (BSTDC) to assess the prevalence of AOD problems among STD clinic patients. Assessing problematic AOD involvement among STD patients was of interest to BSTDC for STD prevention and to OASAS, for new AOD case-finding and early intervention. During fall, 2000, 100 STD patients in each of the 7 full-time BSTDC clinics in New York City were solicited in clinic waiting rooms; eligible patients were screened individually and anonymously with a modified CAGE-A (mCA). The mCA asks 4 questions about problematic AOD use "ever" (i.e., "lifetime") and currently (i.e., "in the past 30 days) rather than "in the past 12 months" of the CAGE and uses two or more "Yes" answers as a "positive" screen. The mCA also asks for age, sex, ethnicity, prior AOD treatment, and interest in an AOD referral. Only 2 of 704 eligible patients refused mCA screening, n = 702. Sixty percent were male, 87.7% Black and/or Hispanic, and 69%, <or=35 years old. Of the sample screened, 30.5% were "positive" on the "ever" and 16.5%, on "the past 30 days," mCA questions. 13.2% reported prior AOD treatment, 1.4% were in AOD treatment or about to start, and <1% wanted an AOD referral. Eight of 10 STD patients currently in AOD treatment screened positive on the "ever" mCA questions. The AOD prevalence rates observed here were deemed high since: 1) CAGE (and CAGE-A) data on general hospital and emergency room admissions showed positive screening rates of only 5-14 % and 2) only an estimated 6-7% of adults in New York have received any formal intervention with an AOD problem, less than half the rate found for treatment alone with the STD patients in this study. The results support implementing AOD screening and intervention services in STD clinics since an estimated 11,000 patients annually would screen positive but now are undetected and untreated. As AOD intervention services also can reduce risky sexual behavior, providing them could expand STD prevention services significantly. Policy, funding, and evaluation issues related to implementing AOD intervention services in STD and other public health clinics also are discussed.