Case: A male, 42 years old, presented to the clinic in June 2012 with “recurrent nocturnal penile erection pain for 1 year, aggravated for 2 months”. The patient had intermittent nocturnal penile erection 2 years ago, with pain and discomfort during erection, and the erection and pain disappeared after waking up, with 1 or 2 episodes per night. In the past 2 months, the symptoms have worsened, with painful erections 3 or 4 times a night. The erection and pain disappeared after waking up to urinate, affecting sleep. He has a poor diet and sleep, and his bowels are regulated. Past history: history of diabetes mellitus for 3 years, now with moderate glycemic control; poor sleep in the last 2 years, with many dreams at night. Denied other medical history. Physical examination: the penis was about 7 cm long, the testes were 15 ml bilaterally, the texture was normal, and no varicocele was palpated. Auxiliary examination: fasting blood glucose 6.8mmol/L, postprandial blood glucose 8.2mmol/L, blood routine, blood coagulation and blood viscosity were not abnormal; sex hormone test: T was 9.26nmol/L, all within the normal range. No abnormality was seen in penile cavernosal ultrasound; cranial MRI: no abnormality was seen. Polysomnography combined with NPT test: painful erection often occurred during rapid eye movement sleep (REM sleep). Diagnosis: sleep-related painful erection Analysis: sleep-related painful erection is a type of abnormal penile erection in which penile pain occurs during erection during sleep. Typical clinical presentation: Patients experience recurrent painful penile erections during sleep, especially during rapid eye movement sleep (REM), and the pain disappears upon awakening, while no painful erections occur during sexual intercourse and masturbation in the awakened state. Accompanying symptoms include recurrent arousals, decreased sleep, daytime anxiety, tension, and irritability. Although the most common concomitant symptom of sleep-related painful erections is anxiety, psychiatric evaluation of this group of patients often does not lead to a diagnosis of psychiatric disorder.