Adolescents’ sexual activity is associated with maternal and child health problems, and sexually transmitted infections including HIV/AIDS. The aim of this study was to assess the sexual behaviour patterns of adolescent schoolgirls and the level of knowledge they have with regard to the prevention and transmission of HIV infection, as well as to determine which factors are associated with their various sexual behaviour patterns. A cross-sectional descriptive survey of 420 adolescent schoolgirls aged 15 to 19 years, from 3 of the 9 secondary schools situated in Petauke District, in rural Zambia, was conducted. The sample of schoolgirls was obtained using a multi-stage systemic sampling technique. Fifty one percent of the sample lived with both parents and 40% had ‘ever had sex’ with the average age at first sexual intercourse being 16 years. The desire to experiment was stated by 48% of the sexually active schoolgirls as being their main motive for engaging in their first act of sexual intercourse. Twenty two percent of the sexually active schoolgirls reported that they were forced into their first act of sexual intercourse. Fifty eight percent of the sexually active schoolgirls had only one sexual partner during their lifetime. Sixty four percent of the sexually active had practiced unsafe sex, yet only 18% of them thought that they were at risk of contracting HIV. Only 49% of schoolgirls used a condom during their last act of sexual intercourse, while 14% of all schoolgirls and 21 % of the sexually active thought that using a condom was a sign of mistrust. A large percentage (65%) of all the schoolgirls thought that the availability of condoms encourages adolescents to engage in sexual intercourse. Sixty nine percent of sexually active schoolgirls had sufficient knowledge regarding how HIV was transmitted but only 31% knew how to prevent contracting HIV and only 18% of those not sexually active knew how to prevent contracting HIV. Almost all schoolgirls (99%) thought that cleaning the vagina after sexual intercourse would not decrease the risk of HIV infection. Magazines and friends were the main 4 source of information on sexual matters, with 51% of the sexually active and 46 % of those not sexually active having these as their main source of information. Seventy one percent of the sexually active reported that they had a regular boyfriend while only 12% of those not sexually active reported having a regular boyfriend. Amongst the sexually active, 6% had a teacher as their regular boyfriend. Eight six percent of schoolgirls had their first act of sexual intercourse with a fellow adolescent and 3% had it with a teacher. The prevalence ratios 1.6 (CI = 1.4-1.8) and 1.4 (CI = 1.2-1.6) indicated that schoolgirls older than 16 years were more likely to have ever had sexual intercourse and to have a regular boyfriend, respectively. It was also shown that schoolgirls who had undergone initiation ceremonies were more likely to have ever had sex, prevalence ratio 1.3 (CI = 1.1-1.6). Given the high level of sexual activity (40%), the increase of sexual activity with age, the high prevalence of risky sexual activity and the low level of knowledge about how to prevent HIV infection, the task of improving sexual education and life skills should be engaged with. Based on the findings of this study, three main recommendations were addressed to the health, educational and community authorities, in relation to the provision of appropriate evidence-based life skills education to both schoolgirls and schoolboys.