An age difference > 5 years in the choice of sexual partner may constitute a risk factor for sexually transmitted infections (STIs), including HIV infection. A sexual and reproductive health survey was carried out on people who consulted for STIs or HIV serology in two health centers in Buenos Aires suburbs, with the aim of providing information for the design of prevention measures and to know if in this area there is an association between the maximum age difference (MAD) in the choice of sexual partner and the acquisition of HIV and/or STIs. A total of 120 patients consulted, 90% (108) performed serology, resulting 15 of them (13.9%) infected with HIV and 46 (42.6%) with syphilis. The MAD with the partner was = 5 years in 65 (54.6%) and > 5 years in 54 (45.4%) of 119 who answered the survey. Men who have sex with men reported a MAD > 5 years more frequently (p = 0.022 OR: 3.59). The risk for HIV increased 9% for each year of age difference with the sexual partner (OR: 1.093). The percentage of urethritis cases was significantly lower in the age group = 25 years. None of the people with urethritis had HIV infection. In conclusion: Men who have sex with men tended to choose their sexual partners with a higher MAD, and a higher MAD was a risk factors for HIV infection.