A cross sectional study was conducted to estimate the prevalence and correlates of suicidal ideation among in-school adolescents in Zambia. Backward logistic regression analysis was conducted to assess the association between relevant predictor variables and suicidal ideation within the last 12 months. A total of 1970 in-school adolescents who participated in the Zambia Global School-Based Health Survey in 2004 responded to the question on suicidal ideation. Overall, 54.0% were males, 40.8% were current drinkers, and 35.9% ever smoked marijuana (cannabis). Altogether 31.3% reported suicidal ideation in the past 12 months (males = 31.1%; females = 31.4%). Being male (OR = 1.05; 95%CI 1.03, 1.05): being <14 years old (OR = 1.21; 95%CI 1.19, 1.23), having been drunk (OR = 1.28; 95%CI 1.27, 1.29). worried (OR= 1.05; 95%CI 1.04, 1.06), sad or hopeless in the past 12 months (OR = 1.02; 95%CI 1.01, 1.03) and ever used marijuana (OR = 1.18; 95%CI 1.17, 1.19) were positively associated with suicidal ideation. Loneliness appeared to be protective (OR = 0.92; 95%CI 0.91, 0.92). All the results, except for ever smoked marijuana and ever been drunk, may have been biased due to non-response to the question on suicidal ideation. A series of cross sectional studies should be conducted to monitor changes in behavioural factors among others ever smoked marijuana and ever been drunk in order to broaden our understanding of factors that may be causing adolescents to seriously consider committing suicide.