Objective Previous research has suggested that gay men facing prostate cancer may be particularly vulnerable to poor illness adjustment. Moreover, although attachment and greater disclosure of sexual orientation have been associated with health outcomes, their associations in this population have been largely unexamined. The purpose of the present study was to investigate whether greater outness about one's sexual orientation significantly mediated the associations between anxious and avoidant attachment and illness intrusiveness among gay men with prostate cancer. Methods Ninety‐two gay and bisexual men who had received a diagnosis of prostate cancer in the past 4 years were recruited for the present study. Self‐report questionnaires assessed demographic and medical variables, attachment, outness level and comfort, and illness intrusiveness. Bootstrapping procedures were used to assess for mediation. Results Results suggested significant associations between anxious attachment, outness comfort, and illness intrusiveness. Less comfort with outness significantly mediated the association between greater anxious attachment and more illness intrusiveness. Avoidant attachment was not significantly associated with illness intrusiveness. Conclusions Findings support the mediating role of the subjective experience of being an out gay man in the association between anxious attachment and illness intrusiveness. These results suggest that facilitating greater comfort with outness would be beneficial for illness adjustment among gay men with prostate cancer whom have more anxious attachment styles. Copyright © 2015 John Wiley & Sons, Ltd.