Objective. Nocturia, a common and bothersome symptom of benign prostatic hyperplasia (BPH), may cause sleep disturbances. Patients with nocturia may have difficulty returning to their normal sleep after repeated episodes of waking and voiding. Therefore, nocturia may have an impact on the circadian rhythm of blood pressure (BP). The association between nocturia and the circadian rhythm of BP was investigated in this study. Material and methods. A total of 100 male patients who had been diagnosed with BPH and 53 healthy male subjects were included in the study. Nocturnal urinary frequency was assessed by means of a questionnaire and recorded in both groups. Ambulatory BP monitoring was performed in all patients over a 24-h period. Results. Patient characteristics and laboratory parameters were similar in both groups. Seventy-five patients (75%) in the BPH group and 20 subjects (37.7%) in the control group were non-dippers, i.e. they did not have a normal nocturnal fall in BP, and this difference was statistically significant (p=0.001). Eighty-nine patients in the BPH group and 13 in the control group had nocturia. Seventy-one patients (79.8%) with nocturia were non-dippers and the difference compared to the patients without nocturia in the BPH group was significant (p=0.003), whereas four patients with nocturia (30.8%) were non-dippers in the control group. Conclusions. Our findings indicate that non-dipping was more prevalent in elderly men with BPH and nocturia. BPH and nocturia may be etiological factors in the pathogenesis of non-dipping, which is an indicator of early cardiovascular disease. Further studies must focus on this relationship and, especially, on whether treatment of nocturia and BPH helps to treat non-dipping or not.