Background: C3 glomerulopathy (C3G) is rare type of glomerulonephritis resulting from the glomerular deposition of C3 due to dysregulation of the alternative pathway of complement. It is further subdivided into C3 glomerulonephritis (C3GN) and dense deposit disease (DDD), depending on the ultrastructural features. C3GN usually presents with a membranoproliferative pattern of injury. Crescents may or may not be present. However, we have noted a severe necrotizing and crescentic glomerulonephritis in a small subset of C3GN patients. Case diagnosis/treatment: We present the clinical features, kidney biopsy findings, complement evaluation, treatment, and follow-up of four C3GN patients. We also compare the findings with four DDD patients with a severe necrotizing and crescentic glomerulonephritis. The patients were young and presented with hematuria and proteinuria. The biopsy was remarkable for the large number of crescents, in association with bright glomerular staining for C3. The patients were treated with steroids/immunosuppressive drugs. Three of the 4 C3GN patients and 2 of the 4 DDD patients showed stable renal function at follow-up. We find remarkable similarities between our C3GN patients with crescents and the previously described entity of juvenile acute nonproliferative glomerulonephritis. Conclusions: To summarize, C3G with a severe crescentic phenotype is rare, affects children and young adults, and has a variable response to steroid and immunosuppressive treatment. It is important to recognize this rare cause of crescentic glomerulonephritis so that appropriate evaluation and treatment can be carried out.