INTRODUCTION: With earlier prostate cancer (PCa) diagnosis and an increased focus on survivorship, post-treatment sexual quality of life (QoL) has become increasingly important. Research and validated instruments for sexual QoL assessment based on heterosexual samples have limited applicability for men-who-have-sex-with-men (MSM). AIM: We aimed to create a validated instrument for assessing sexual needs and concerns of MSM post-PCa treatment. Here we explore post-PCa treatment sexual concerns for a sample of MSM, as the first part of this multi-phase project. METHODS: Individual semi-structured interviews were conducted with 16 MSM face-to-face or via Internet-based video conferencing. Participants were asked open-ended questions about their experiences of sexual QoL following PCa. Interviews were recorded, transcribed verbatim, uploaded to NVivo 8(TM) , and analyzed using qualitative methodology. MAIN OUTCOME MEASURE: We have conducted semi-structure qualitative interviews on 16 MSM who were treated for PCa. Focus was on post-treatment sexual concerns. RESULTS: The following themes were inductively derived: (i) erectile, urinary, ejaculation, and orgasmic dysfunctions; (ii) challenges to intimate relationships; and (iii) lack of MSM-specific oncological and psychosocial support for PCa survivorship. Sexual practices pre-treatment ranked in order of frequency were masturbation, oral sex, and anal sex, an ordering that prevailed post-treatment. Sexual QoL decreased with erectile, urinary, and ejaculation dysfunctions. Post-treatment orgasms were compromised. Some single men and men in non-monogamous relationships reported a loss of confidence or difficulty meeting other men post-treatment. Limited access to targeted oncological and psychosocial supports posed difficulties in coping with PCa for MSM. CONCLUSIONS: The negative impact on sexual QoL can be severe for MSM and requires targeted attention. Penile-vaginal intercourse and erectile function have been the primary focus of sexual research and rehabilitation for men with PCa, and do not adequately reflect the sexual practices of MSM. Our findings suggest that future research dedicated to MSM with PCa is needed to incorporate their sexual practices and preferences specifically into treatment decisions, and that targeted oncological and psychosocial support services are also warranted.