Adolescents' risky sexual behaviours (RSB) are detrimental to their sexual and reproductive health (SRH) well-being and present a serious public health threat, particularly in low- and middle-income countries (LMICs). This study aims to assess RSB among Grade 12 school-going adolescents after exposure to comprehensive sexuality education (CSE). This study was conducted in Kitwe district, Zambia. This cross-sectional study included 807 Grade 12 pupils at 13 selected secondary schools. Data were collected using a structured questionnaire. Proportionate probability sampling involving 13 schools was employed. Risky sexual behaviours binary outcome variables were based on transactional sex, sex while drunk, multiple sexual partners, age-disparate sexual relationships, and condomless sex. We conducted univariate and bivariate analyses to summarise sociodemographic factors and fitted binary and multivariable logistic regression models. The prevalence of RSB was 40.4%. Drinking alcohol (adjusted odds ratio [AOR] = 20.825; 95% CI [6.7-64.489]); ever had sex (AOR = 9.024; 95% CI [1.953-41.704]); school location (AOR = 6.50; 95% CI [1.61-26.24]); living with mother only (AOR = 4.820; 95% CI [1.328-17.493]); sex (male) (AOR = 2.632; 95% CI [1.469-4.713]), watching pornography (AOR = 1.745; 95% CI [1008-3.021]); religion (AOR = 0.472; 95% CI [0.250-0.891]) and attending religious functions (AOR = 0.317; 95% CI [0.118-0.848]) were significantly associated with RSB. Of the sexually active pupils, 221 (67.7%), 64 (19.6%) and 41 (12.5%) were in the low, medium and high-risk categories, respectively. Close to half of the respondents engaged in RSB. This is a significant number that needs intervention. The CSE programme needs to be linked with structural programmes that address the social drivers of RSB among adolescents.Contribution:The study provides a backdrop for evaluating current CSE strategies in LMICs.