We report 2 seminomas with conspicuous numbers of signet ring cells. The tumors occurred in men, 24 and 69 years of age, who presented with testicular masses; 1 seminoma was a component of a mixed germ cell tumor and the other was pure. The signet ring cells occurred in a multifocal fashion in areas of otherwise typical seminoma and comprised approximately 70% and 10%, respectively, of the tumors. They had large, translucent to clear cytoplasmic vacuoles that compressed the nuclei to a peripheral crescent. In 1 case, the vacuoles contained numerous refractile, nonpolarizable globular deposits that were shown to be glycogen on the basis of periodic acid-Schiff stain positivity that was abolished by pretreatment with diastase; in the second case, they mostly appeared "empty" and lacked periodic acid-Schiff positivity. The signet ring cells were mucicarmine, cytokeratin (AE1/3) and alpha-fetoprotein negative, but positive for OCT3/4 and CD117, the latter 2 being expected for seminoma cells. A review of 30 randomly selected seminomas identified very rare, inconspicuous signet ring cells in 43%. The presence of prominent signet ring cells in seminoma may cause confusion as it has not been described previously in detail, and a variety of neoplasms, particularly metastasis, may be considered. The description of this phenomenon expands the known morphologic spectrum of the most common testicular neoplasm.