Objective: To report the first systematic investigation of the cognitive effects of luteinizing hormone-releasing hormone (LHRH) analogues in male patients, as LHRH analogues have been associated with memory impairments in women using these drugs for gynaecological conditions. Patients and methods: Eighty-two men with extraprostatic prostate cancer were randomly assigned to receive either continuous leuprorelin, goserelin (both LHRH analogues), cyproterone acetate (a steroidal antiandrogen) or close clinical monitoring. These patients underwent cognitive assessments at baseline and before starting treatment (77), and then 6 months later (65). Results: Compared with the baseline assessments, men receiving androgen suppression monotherapy performed worse in two of 12 tests of attention and memory; 24 of 50 men randomized to active treatment and assessed 6 months later had a clinically significant decline in one or more cognitive tests but not one patient randomized to close monitoring showed a decline in any test performance. Conclusion: Pharmacological androgen suppression monotherapy for prostate cancer may be associated with impaired memory, attention and executive functions