Objective: The objective of this paper was to assess students' attitudes towards school-based sex and relationships education (SRE). Design: This study featured a cross-sectional survey design. Method: A sample of 715 students from two districts in Tanzania completed a survey questionnaire assessing various aspects related to their attitudes towards SRE. Results: Results show that the overwhelming majority (more than 80%) of students supported the provision of SRE in schools and the inclusion of a wide range of SRE topics in the curriculum. The majority of students wanted the teaching of SRE in schools to begin early during primary education (ages 10-14). Nevertheless, the majority of students objected to the inclusion of some of the SRE topics that are commonly regarded as controversial, including homosexuality and masturbation. Students' attitudes towards SRE and specific topics were associated with participants' sex, age and religious affiliation. Conclusion: The results of this study should encourage policy makers and researchers in Tanzania to advocate for the provision of comprehensive sex education in schools.