Do health-related knowledge, beliefs and self-efficacy differ between women with and without polycystic ovary syndrome (PCOS)? Women with PCOS felt at greater risk for adverse health outcomes, yet believed a healthy lifestyle was less beneficial to prevent weight gain relative to a comparison group. Diet and physical activity are often used to treat PCOS, but there are high attrition rates and less engagement in self-help methods. It is unclear whether there are unique psychosocial considerations in PCOS that should be incorporated into these interventions. This cross-sectional study enrolled 475 women with (N = 255) and without PCOS (N = 220). Female participants were recruited through paper and web-based advertisements across the US (mean age: 28.1 ± 5.4 years). Participants were either diagnosed with PCOS by a healthcare professional (PCOS group) or had self-reported regular menstrual cycles (comparison group). A reliable and valid online instrument about health-related knowledge, beliefs and self-efficacy was administered to these participants. Most women with PCOS had a basic understanding of nutrition (96%), but had misconceptions about diagnostic criteria for PCOS (≥86%). PCOS was associated with greater perceived susceptibility for disease and weight gain and poorer perceived control over these health outcomes (all P < 0.05), in relation to the comparison group. Women with PCOS also perceived fewer benefits of healthy behaviors on weight gain (P = 0.03) with less than half of the PCOS group attempting to follow government diet recommendations (47%). There were no differences in the self-efficacy of dietary behaviors between groups. It is likely that participant self-selection occurred due to the nature of recruitment in this study and results may have limited generalizability since most participants identified as Caucasian. Additionally, it is unclear whether some results may be clinically meaningful due to small effect sizes. These findings support that behavioral interventions should incorporate the unique psychosocial considerations associated with PCOS to encourage patient participation in lifestyle interventions. This manuscript was partially supported by Cornell University Human Ecology Alumni Association and College of Agriculture and Life Sciences Alumni Association. The authors have no competing interests. NCT01859663.