Abstract
BACKGROUND: Cross-generational sexual relationships keep exposing more young persons to sexually transmitted infections, psychosocial and emotional trauma and various forms of abuse and have been linked with more cases of human immunodeficiency virus infection within the sub-Saharan Africa region; hence, the need to assess the knowledge and prevalence of cross-generational sexual relationships among undergraduates of a Nigerian institution. METHODOLOGY: The study employed a descriptive cross-sectional survey design, utilising a four-stage sampling technique to select 390 undergraduates across the institution’s 13 faculties. Data were collected using tested, semi-structured and self-administered questionnaires. The data collected were analysed using IBM SPSS version 23. Chi-square tests were used to determine the associations at p < 0.05. RESULTS: The mean age of the participants was 21.44 ± 2.62 years. The prevalence of cross-generational sexual relationships was 13.1%, 40.8% had poor knowledge, and 68.1% of the respondents practising cross-generational sexual relationships were unwilling to quit. Marital status (p = 0.008), family structure (p = 0.019), and level of study (p < 0.01) were significantly associated with the prevalence of cross-generational sexual relationships among the study population. CONCLUSION: This study reveals a significant prevalence and poor structure of cross-generational sexual relationships among undergraduate students, primarily driven by low-income family structure, relationship status and peer pressure. To address cross-generational sexual relationships, comprehensive sexual education, poverty alleviation initiatives, and mentorship programmes are recommended. These interventions can reduce prevalence, prevent harmful consequences, and promote healthier relationships among young individuals, especially in tertiary institutions. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12889-025-25639-z.