Lactose intolerance (LI), a consequence of decreased or absent intestinalβ-galactosidase activity is common in the pediatric population. Treatment generally includes dietary lactose restriction, use of exogenous lactase or a combination of the two. To evaluate the effectiveness of these therapies we interviewed 100 patients (58 male, 42 female, aged 4-19 y, mean=11.0 y) 6-36 months after diagnosed as being LI by a positive hydrogen breath test, using a standardized questionnaire. The interview included questions about initial symptoms, present diet, use of exogenous lactase and present symptoms. Participants also graded their symptom severity. Of the 100 subjects interviewed, 60% were on a lactose-free diet, 67% used lactase tablets, and 42% used both. Data analysis showed a significant (p<0.01) reduction in the frequency of abdominal pain, diarrhea, gassiness, bloating and abdominal distention, whether they were on a lactose-restricted diet or taking lactase tablets. Diet restriction alone resulted in a significant decrease in the reported symptoms of abdominal pain by 50%, diarrhea by 83%, bloating by 66%, gassiness by 60%, and abdominal distension by 66%. Lactase tablets alone resulted in a significant decrease in abdominal pain by 47%, diarrhea by 60%, bloating by 41%, gassiness by 44% and abdominal distension by 66%. However, children who were both lactose-restricted and used lactase tablets had an even greater decrease of symptom occurrence (p<0.001) when compared to either alone. The results describing severity of symptoms were similar, showing a significant (p<0.01) reduction of abdominal pain, diarrhea and gassiness employing either therapy alone. Combining therapies resulted in a more significant (p<0.001) reduction of symptom severity than either alone. Use of single or combined therapies however, had no effect on the occurrence or severity of bloating and abdominal distention. Conclusions: A large percentage of pediatric patients continue to utilize treatment for their lactose intolerance up to 3 years following diagnosis. Treatment of lactose intolerance by either dietary restriction or use of exogenous lactase causes a significant reduction of symptoms and symptom severity, and the efficacy of these modalities increases significantly when these two modalities are combined.