We report on 20 Brazilian children under 6 years of age with very-early-onset inflammatory bowel disease naive to treatment. The clinical, laboratory, and histopathologic findings at diagnosis and outcomes were reviewed: 13 had ulcerative colitis (UC) and 7 had Crohn disease (CD). The final diagnostic pattern was as follows: 4 children had neonatal-onset (1 UC and 3 CD), 8 had infantile subtype (4 UC and 4 CD), and 8 had UC beyond the neonatal and infantile period. Both forms of inflammatory bowel disease were severe and extensive at diagnosis, with a high prevalence of bloody diarrhea, reflecting the colonic location of the disease. UC was predominantly pancolonic, CD was isolated in the colon and associated with perianal disease. Children with CD were younger than those with UC, were significantly more nutritionally impaired, and had more complications. This study shows that very-early-onset inflammatory bowel disease has an aggressive clinical course with 2 distinct phenotypes, UC and CD, with differences in severity, clinical behavior, and inflammatory pattern but with a preponderance of colonic involvement in both types.