OBJECTIVE: To explore ideas of truck drivers and villagers from rural Tanzania about heterosexual anal sex (HAS) and the associated health risks. METHODS: Qualitative study using 8 in-depth interviews (IDIs) and 2 focus group discussions (FGDs) with truck drivers and 16 IDIs and 4 FGDs with villagers from the Morogoro region. Study participants included 24 women and 46 men. Data analysis was performed thematically employing standard qualitative techniques. RESULTS: Reasons why men would practice HAS included sexual pleasure, the belief that anal sex is safer than vaginal sex, alternative sexual practice, exploration and proof of masculinity. Reasons why women would practice HAS included financial need, retaining a partner, alternative for sex during menses, pregnancy prevention and beauty enhancement because HAS is believed to 'fatten the female buttocks'. Most participants believed that condoms are not needed during HAS. This was linked to the ideas that infections only 'reside in wet places' (vagina) and that the anus is not 'conducive' for condom use; condoms reduce 'dryness' and 'friction' (pleasure) and may 'get stuck inside'. CONCLUSIONS: The study participants reported practices and ideas about HAS that put them at risk for HIV and sexually transmitted infections. Greater attention to education about HAS is urgently needed in Tanzania, where this sexual practice is still regarded as a taboo. This study offers useful information that could be included in sex education programmes.