To define the role of human caliciviruses (HuCVs) in severe childhood gastroenteritis, fecal and paired serum samples from 233 Peruvian children hospitalized with gastroenteritis (case patients) and fecal samples from 248 control subjects were evaluated. Overall, 128 case patients (55%) demonstrated HuCV infection by either fecal (n = 81 [35%]) or serological (n = 96 [41%]) testing. HuCVs were more prevalent in fecal samples from case patients than those from control subjects (35% vs. 13%; P < .001). HuCV infection was more prevalent among case patients without another pathogen than in those who had a coinfecting pathogen (77% [40/52] vs. 49% [88/181]; P < .001). HuCVs appear to be an important cause of gastroenteritis in Peruvian children.