The primary objective of the clinical trial is the assessment of the acceptability of the new Pentasa formulation - PentasaR Sachets in comparison with the reference PentasaR tablets 500 mg in children with Crohn's disease. After the screening period (which includes medical history, physical examination, basic haematology, serum chemistry , urine analysis and stool microbiology , PCD Activity Index )patients will receive (visit I) Pentasa sachets 1g or Pentasa tablets 500mg for next 4 weeks according to the randomisation scheme in common dose 2× 1 g of PentasaR Sachets 1 g or PentasaR tablets 500 mg. The formulation of Pentasa will be switched at Visit 2, patients will receive the medication for next 4 weeks. Patients will record the acceptability of the both forms of the medication.

In 6 patients from each group (selected by the randomization), stool and urine will be taken to assess concentrations of mesalazine and N-acetylmesalazine during Visit 2 and Visit 3. Adverse events will be recorded during the whole course of the treatment period.

Inclusion Criteria:

• Established diagnose of Crohn's disease
• Age 8-18 years, both sexes
• Weight above 40 kg
• Oral maintenance treatment with 5-ASA and any concomitant antinflammatory medication (maintained at the same dose during the study) before inclusion is permitted,
• written informed consent obtained (patient and his/her guardian)

Exclusion Criteria:

• Patients with a history of allergy to salicylates
• Patients with known significant hepatic or renal function abnormalities
• Positive enteric pathogens in stool (Salmonella, Shigella, Yersinia, Campylobacter)
• Pregnant or lactating women
• Patients with a known history of disease, including mental/emotional disorder, that would interfere with their participation in the study,
• Patients who participated in another clinical study in the last 3 months,
• Patients who are unable to comply with the requirements of the protocol
• Patients who are unable to fill in the diary cards