Once Versus Twice Daily Mesalamine to Induce Remission in Pediatric Ulcerative Colitis

Inclusion Criteria: 1. Children 6-18 years of age, weight least 15kg. 2. Diagnosis of UC, established by the presence of accepted clinical, radiologic, endoscopic and histologic criteria. 3. Mild to moderate disease activity at the time of enrolment as judged by the Pediatric UC Activity Index (PUCAI) score 10-55 points. 4. In general good health (other than the diagnosis of UC), based on medical history, physical examination, and screening laboratory results. 5. Infectious colitis excluded by stool cultures, ova and parasite examination and Clostridium difficile assay. 6. Ability and acceptance to participate in the study and follow study procedures, as evidenced by a parent/legal guardian signing a written informed consent and the child providing assent. Exclusion Criteria: 1. Weight \<15 kg at enrolment 2. Patients whose disease is confined to the rectum (i.e. proctitis). 3. Fever \>38.5 degrees. 4. Patients with Crohn's colitis or with IBD type unclassified (IBD-U) according to Montreal classification. 5. Treatment with oral 5-ASA oral preparation with at least 50mg/kg/day \> 3 days within 7 days prior to screening visit. Patients who are treated with 5-ASA \<50mg/kg/d may be enrolled as their dose will be increased significantly in this trial. A sensitivity analysis is planned including only 5-ASA naïve children. 6. Exacerbation associated with infectious organism in the stool. 7. Current treatment with steroids (any dose) or the need for steroid therapy as judged by the responsible gastroenterologist. 8. Rectal therapies (suppositories, foams, enemas etc) of all kind are allowed if the dose and frequency has remained stable during the previous 30 days prior to the screening visit. No changes are allowed after randomization and until completion of the study. 9. Treatment with immunomodulatory therapy including, but not limited to: 6 mercaptopurine (6-MP), azathioprine, cyclosporine, tacrolimus, rosiglitazone or methotrexate, is allowed if the dose and frequency has remained stable during the previous 90 days prior to the screening visit. No changes are allowed after randomization and until completion of the study. 10. Treatment with biologic therapy including, but not limited to: infliximab, certolizumab, adalimumab within 90 days prior to screening visit. 11. Pregnancy. All female patients of childbearing potential will undergo urine pregnancy testing at screening, must not be lactating, and willing to use acceptable contraception if sexually active. 12. Known allergy to 5ASA, salicylates, or aminosalicylates. 13. Existence of current renal disease, or a screening blood urea nitrogen (BUN) or creatinine value that is \> 1.5 times the upper limit of the age appropriate normal. 14. Existence of current hepatic disease, or liver tests (ALT, AST, T-Bili) that are \> 2 times the upper limit of normal, or the existence of Primary Sclerosing Cholangitis (PSC). 15. History of recurrent pancreatitis. 16. Any other laboratory or clinical condition that the investigator considers clinically significant that would impact the outcome of the study or the safety of the patient.