Color Doppler sonography represents the gold standard imaging technique for the diagnosis and grading of varicocele. However, the diameter of the pampiniform venous plexus and, consequently, the grading of varicocele is affected by several factors such as exercise, physical activity, and standing position. It is usually disregarded that all the previously mentioned factors may differently affect diagnostic outcomes in the evening compared with the morning. In this light, the current study was designed to point out the best timing for performing sonographic evaluations. The study was conducted on the subjects attending diagnostic sonography in Baqiyatallah Hospital, Tehran, Iran, from January 2018 to January 2019. A total of 275 patients diagnosed with varicocele were selected for assessment by color Doppler sonography both in the morning and evening. An expert radiologist measured the diameter of pampiniform plexus veins and graded varicocele. Data analysis was performed by SPSS. A total of 275 patients were studied, with a mean age of 23 years. The mean diameter of the veins was 3.51mm in the morning and 4.02mm in the evening (P < 0.05). Moreover, 23 patients (41.8%) who were classified as Grade I during the morning evaluation were reclassified as Grade II in the evening. Of the rest, 44 patients (48.8%) of those assessed as Grade II in the morning, were upgraded to Grade III during the evening assessments. We suggest the end of the day for the sonographic evaluation of vein size measurement and grading of varicocele disease rather than in the morning.  Kulcsszavak: varicocele, color Doppler, ultrasound, pampiniform venous plexus