To measure the prevalence and severity of Generalised Anxiety Disorder (GAD), hypo- and hypercortisolaemia, and their association in a sample of prostate cancer (PCa) patients, 97 Australian PCa patients completed a background questionnaire and the GAD-7, and provided a sample of saliva collected 30–45 min after waking. The mean GAD7 score was 9.67 (SD = 3.09), and prevalence rates for current anxiety were higher than those reported for non-PCa males of a similar age. Mean salivary cortisol concentrations (30.78 nmol/L, SD = 13.97 nmol/L) were also higher than for age-comparative non-PCa men. There was a significant inverse correlation between GAD and cortisol (r = −. 209, p <.05), and four subgroups of GAD-cortisol patients were able to be identified, with evidence of both hyper- and hypocortisolaemia. These findings provide initial neurobiological evidence of the chronic and profound nature of stress experienced by PCa patients, and also suggest a possible measure that might be used to identify most at-risk PCa patients.