• Two male patients were initially seen with loin pain and gross hematuria. Both had normal renal function. Findings from physical examination and laboratory evaluation showed no evidence of nephrolithiasis, papillary necrosis, or renal vascular disease. Renal biopsy results showed minimal to mild mesangial hypercellularity of the glomeruli of both patients, with positive immunofluorescence in the mesangium to IgA and C3 in one patient and to IgM and C3 in the other patient, findings consistent with IgA and IgM nephropathy, respectively. We conclude that both IgA and IgM nephropathy may be initially seen with loin pain and gross hematuria, and these disorders should be considered in the differential diagnosis of this syndrome.