This paper aims to delineate the cognitive, emotional, and behavioural responses of women with polycystic ovary syndrome (PCOS) to their illness by applying the Common-Sense Model of Self-Regulation (CSM) to their health behaviour. An online cross-sectional design was used to examine the relationship between participants’ illness perceptions (illness identity, consequence, timeline, control, and cause) and emotional representations of their PCOS, and their health behaviours (diet, physical activity, and risky contraceptive behaviour). The participants were 252 women between the ages of 18 and 45 years, living in Australia, and self-reporting a diagnosis of PCOS, recruited through social media. Participants completed an online questionnaire regarding illness perceptions as well as their diet, physical activity, and risky contraceptive behaviour. Illness identity was positively associated with the number of maladaptive dietary practices (B= 0.71, 95% CI: 0.003, 0.138;p= 0.04), and perception of longer illness duration was associated with reduced physical activity (OR = 0.898, 95% CI: 0.807, 0.999;p= 0.49) and risky contraceptive behaviour (OR = 0.856, 95% CI: 0.736, 0.997;p= 0.045). The limitations of the study include all data being self-reported (including PCOS diagnosis), and the potential for analyses of physical activity and risky contraceptive use being underpowered due to reduced sample sizes. The sample was also highly educated and restricted to those who use social media. These findings suggest that illness perceptions may play a role in influencing health behaviour in women with PCOS. A better understanding of the illness perceptions of women with PCOS is needed to increase health-promoting behaviour and improve health outcomes for women with PCOS.