The observed increase of sexually transmitted diseases (STD) in Cuba aroused the interest of carrying out a study aimed at exploring risky sexual behaviours and attitudes, and histories of STD. A crosswise descriptive study was undertaken using a randomized sample taken from the universe of adolescent students in the City of Havana during 1995-96 school year. The sample was made up by 2,793 teenagers aged 11-19 years (1,370 females and 1,423 males). Previously trained experts linked to this field collected data by means of a structured interview which had been drawn up for this end. It was confirmed that more than half of adolescent students did not use condom in their sexual intercourse 57% had more than one sexual partner along the year, 40% believed it was difficult to keep only one partner whereas 35% had more than one sexual partner at the same time. Risk and protected sexual habits were noticed, with 39% for oral-genital and 21.4% for genital-anal. 22% for the interviewed adolescent said they had histories of STD.