INTRODUCTION: Rates of sexually transmitted infection (STI) are rising in the USA, yet STI risk remains under-addressed by providers, even in HIV care, and with high-risk patients. We interviewed primary care patients living with and without HIV regarding circumstances surrounding sexual risk behavior to identify opportunities for providers to address and reduce STI risk. METHODS: We conducted semi-structured 1:1 interviews with patients living with and without HIV reporting ≥ 1 sex partner and varying STI exposure risk in the past 12 months from four geographically diverse US HIV and primary care clinics. We audio-recorded, transcribed, and coded interviews by circumstance type, using double-coding to ensure inter-coder reliability. We used Fisher's exact and T tests to determine associations with demographic/risk factors. RESULTS: Patients (n = 91) identified a mean of 3 of 11 circumstances. These included substance use (54%), desire for physical/emotional intimacy (48%), lack of HIV/STI status disclosure (44%), psychological drivers (i.e., coping, depression; 38%), personal dislike of condoms (22%), partner condom dislike/refusal (19%), receiving payment for sex (13%), and condom unavailability (9%). Higher proportions of those who were high STI-exposure risk patients, defined as those with ≥ 2 sex partners in the past 3 months reporting never or sometimes using condoms, reported disliking condoms (p = .006); higher proportions of the high-risk and moderate-risk (≥ 2 partners and condom use "most of the time") groups reported substance use as a circumstance (p = .04). CONCLUSION: Circumstances surrounding perceived STI exposure risk were diverse, often overlapping, and dependent on internal, environmental, and partner-related factors and inadequate communication. Meaningful care-based interventions regarding HIV/STI transmission behavior must address the diversity and interplay of these factors.