RESUMO
Cystinuria is a disease characterized by the excessive elimination of cystine and of dibasic amino acids (lysine, arginine, and ornithine) through urine of homozygotes. This study included 6 children complaining of abdominal pain with or without hematuria. The existence of renal radio-opaque lithiasis was confirmed in 5 of them and in the sixth, it was vesical. The clinical and analytic data were practically normal with the exception of the qualitative test of the amino acid urinary excretion that showed increase in urinary excretion of cystine. Likewise, percentages of tubular reabsorption were pathological in all the patients showing values between 35.4% and 74%. The diagnosis of systini-lysinuric lithiasis was established through amino acid excretion study in the six patients which was below normal; it fluctuated between 36% and 74%. Lysine, together with cystine, was the most frequently affected.