Studies on sexually transmitted diseases (STD) during the previous years in Mexico are discussed. The information sources were: a) Surveys among commercial sex workers. Since 1990, 1,386 women have been studied in four federal states through structured questionnaires and laboratory tests. Prevalence of different STD's has been significant (syphilis (VDRL, FTA-abs) 23.7%; chlamydiosis (Ag IF) 12.9%; gonorrhea (Ag, ELISA) 11.5%; anti-HBs 11.0%; herpes 1,2 (IgM) 9.3%, HBsAg 5.7%. Frequency of HIV (ELISA, Western blot) has been low; 0.5%. In 1994, 662 women were studied in Mexico City, with different laboratory techniques for chlamydiosis and gonorrhea (culture), hepatitis B (anticore antibodies) and herpes (total antibodies) with the following results: syphilis 1.5-12%; chlamydiosis 10.8-11.7%; gonorrhea 0-5.9%; hepatitis B 0-7.1%; herpes 44.7-78%; and HIV 0-1.4%. b) Surveys among men with homosexual and bisexual practices. 325 subjects have been studied in three federal states using methods similar to those of the 1990 survey. Contrasting with results among women, HIV prevalence was found to be high; (18.8%), and considerable for other STD's: anti-HBsAg 28.6%, syphilis 34.9%, recent herpes 10.9%, HBsAg 5.0%, chlamydiosis (Ag, IF) 4.3%, herpes simplex 1,2 (Ag, IF) 4.7%, gonorrhea (Ag, ELISA) 2.8%. c) Patient clinical studies. The clinical interrelationship between different STD and HIV infection has been studied; clinical differences are described between patients with condylomata or syphilis depending on HIV serostatus. Implications of the interrelationship between different STD's and HIV infection for the prevention and control of these diseases are discussed.