Objectives: To understand women's and men's motivations for entering into cross-generational relationships and to examine how their risk perception for sexually transmitted infections (STIs) and human immunodeficiency virus (HIV) affects sexual decision-making and condom use. Methods: A total of eight focus groups were conducted with women aged 15 -- 19 and 28 indepth interviews were carried out with men aged 30 years and older in Nairobi, Mombasa, Kisumu, and Meru. Participants discussed motivations for entering into non-marital, crossgenerational relationships, perceived risks, relationship dynamics, and circumstances under which older men and younger women meet. Data analysis highlighted common and divergent themes on cross-generational relationships and the risks associated with them. Results: According to study participants, Kenyan men who pursue younger women do not fit a "sugar daddy" stereotype; rather they come from a variety of social and professional backgrounds. Young women actively seek partners who are willing to spend money on them whereas men look for partners who are well mannered, need money and have certain physical attributes. Women's primary incentive for engaging in cross-generational relationships is financial and material gain while men seek younger partners for sexual gratification. Pressure from peers to fit in and some family members to secure financial assistance from older partners can compel women to engage in cross-generational relationships. Although some peer groups support and encourage such relationships, other groups, especially wives, same-aged boyfriends and parents, disapprove of them. As a result, cross-generational couples are often preoccupied by the threat of discovery. Risk perception for STIs/HIV is low and couples rarely use condoms. Conclusions: Most cross-generational couples underestimate their risk for infection from STIs/ HIV. Young women believe that older men are low-risk partners because they are less likely to be promiscuous and more likely to remain faithful to younger partners and wives. Men believe that young partners are innocent and sexually inexperienced. Material gain, emotional factors, sexual gratification, and recognition from peers override the risk for STIs and HIV infection. Condom use is low and young women's ability to negotiate use is compromised by age disparities and economic dependence. Study findings suggest several programmatic strategies for targeting young women and older men. Behavior change communication campaigns should educate women and men about the increased risk of STIs/HIV associated with cross-generational relationships. Programs should also promote safer sexual practices, such as consistent condom use, within relationships. Campaigns could employ positive role models to encourage young women to seek safer alternatives to cross-generational relationships and decrease peer pressure among men to pursue such relationships. Long-term interventions include improving young women's access to educational and career opportunities, and working with communities to determine the best approach for changing social norms and the acceptability of cross-generational relationships.