Purpose Insomnia symptoms are commonly experienced by men after prostate cancer (PCa) treatment. Here we explored how sleep hygiene behaviours and psychological symptoms are associated with insomnia symptoms in PCa patients. Methods An online survey was posted on social media and sent to mailing lists of PCa and general cancer organisations. The survey collected information on demographic, sleep hygiene, and psychological symptoms using validated questionnaires. Results Data from 142 participants were compared based on the absence (age = 68.3 +/- 8.9 years) and presence (age = 66.6 +/- 9.0 years) of insomnia symptoms. Participants with insomnia symptoms had significantly higher levels of anxiety, depression, fatigue, and sleepiness as well as poorer sleep hygiene than those without insomnia symptoms. Control variables (age, number of comorbidities, and BMI) accounted for 11.9% of the variance in insomnia symptoms. Including treatment history contributed to an additional 1.6% of the variance in insomnia symptoms. Adding sleepiness, fatigue, anxiety, and depressive symptoms to the model explained an additional 44.6% of the variance in insomnia symptoms. Furthermore, including the sleep hygiene item 'I think, plan, or worry when I am in bed' and 'I sleep in an uncomfortable bedroom' explained an additional 3.6% of the variance in insomnia symptoms. Conclusions Poor sleep hygiene, fatigue, sleepiness, anxiety, and depressive symptoms were all associated with worse insomnia symptoms in PCa patients. Improving sleep hygiene and treating psychological conditions may potentially help prevent and/or alleviate insomnia symptoms in PCa patients.