Twenty-two cases of sucrase-isomaltase deficiency (SID) were observed over a period of 20 years. Since 1977 delay of introduction of sucrose and its decrease in infants' diets have modified the symptomatology. In general, onset of diarrhea has not taken place immediately but 15 days to 2 months after introduction of sucrose. Out of 12 cases with dehydration, five occurred 3 to 7 months after the beginning of sucrose diet. Hypotrophy was not constant (11 of 22 cases), thus diagnosis was delayed in 17 of 22 cases. A yellow complexion due to rising carotene levels in the blood is a striking feature. Because of falsely positive sucrose load tests (four out of 14 nonSID infants) and failure of the hydrogene breath test (one out of five studied cases), disaccharidase determination remains the key to diagnosis. Despite the genetic difference symptoms seem to depend on infant feeding practices.