The primary hyperoxalurias (PH) are inborn errors of metabolism resulting in increased endogenous production of oxalate leading to excessive urinary oxalate excretion. To date, three distinct hereditary enzymatic deficiencies have been linked to PH, namely, PH type 1 (PH1), type 2 (PH2), and type 3 (PH3). Descriptive cohort study was performed on infants & children with primary hyperoxaluria (PH1) presenting to Cairo University Center of Pediatric Nephrology and Transplantation and hepatology clinic to characterize the clinical presentation of patients in various age groups with respect to both renal and systemic involvement and to report any complications of systemic oxalosis. This study included 15 patients with PH1 during 15 months duration. The median age was 7 years (ranged from 3 months to 18 years). About 43% were diagnosed before the age of 5 years. Four patients (26.6%) were symptomatic during infancy. Twelve children (80%) had already reached end-stage renal disease. Two cases (13%) had systemic manifestations. Nephrolithiasis and/or nephrocalcinosis were present in all patients. PH1 is heterogeneous disease with wide variations of the clinical spectrum. Early diagnosis is imperative but is often delayed or overlooked.