Background: A significant proportion of youth is infected by HIV and other sexually transmitted infections mainly through sexual intercourse, while the prevalence of unwanted pregnancies is rising. Objective: To describe knowledge, attitude and practice and factors influencing sexual relationships and contraceptive practice among the youth in Kisumu town in western Kenya. Methods: A descriptive cross-sectional study using a semi-structured questionnaire, key informant interviews, focus group discussions and informal conversations was carried out. The sample population of 388 youth aged 15 – 24 years was determined by simple random cluster sampling. Quantitative data were analysed using SPSS computer package. Results: The majority of the youth are sexually experienced (73.5%) with most of the first sexual experiences occurring within the 15-19 years age group. There is a high level of knowledge (99.2%) of contraceptive methods and a positive attitude towards contraception. However, the level of contraceptive use is relatively lower (57.5%) even for the sexually active. Factors influencing this practice are associated with the individual’s background as well as health delivery systems and policy. Conclusion: There is a wide disparity between contraceptive knowledge and practice, which needs to be bridged. There is need to review policies and practices regarding reproductive health, sexuality and family life education.