The primary hyperoxalurias (PH1 and PH2) are rare defects of oxalate overproduction. There are only 24 reported cases of PH2, which is characterized by raised urine oxalate and L-glycerate. We describe 13 previously unreported children with PH2, representing the largest single-centre cohort in the world. DNA samples were tested for a common mutation and four other documented mutations in the gene encoding the enzyme glyoxylate reductase/hydroxypyruvate reductase (GRHPR). Two of the five kindred showed homozygosity for two different mutations in the GRHPR gene. The genetic defect was not identified in the other three families. The median age at diagnosis of PH2 was 1.7 years. Five children presented with nephrolithiasis between 0.8 and 9 years. Haematuria was common, but urinary tract infection and nephrocalcinosis were not. All had normal renal function at diagnosis, and only 1 patient had a significant decline in glomerular filtration rate. We conclude that all children with nephrolithiasis secondary to hyperoxaluria should have urinary glycerate measured, as PH2 may be more prevalent than currently estimated. DNA mutational analysis may be useful in supporting the diagnosis.