The aim of this study was to determine the role of surgery in the treatment of abdominal B-cell non-Hodgkin's lymphomas (B-NHL) in children. We analyzed the effect of surgical variables of initial laparotomy and second-look surgery on event-free survival (EFS) of 177 patients with abdominal B-NHL enrolled into the three consecutive multicenter trials NHL-BFM 81, NHL-BFM 83, and NHL-BFM 86. The therapy regimen was comparable in all 3 trials as well as the overall outcome of the patients. Patients with stage II and complete resection received 3 courses of therapy (4 in trial NHL-BFM 81), patients with stage II not resected, stage III, and stage IV received 6 courses of therapy (8 in trial NHL-BFM 81). An initial laparotomy was performed in 161 patients, in 59 of them as an urgent procedure. Complete resection of the abdominal primary was performed in 43 patients, 40 of them had a localized bowel tumor. The probability of EFS (pEFS) at 5 years is 95%, 69%, 62%, and 67% for patients with complete resection, subtotal resection (n = 36), partial resection (n = 21), or biopsy only (n = 61), respectively. Complete resection was achieved in 30 out of 40 patients with stage II, but only in 12 of 113 and 1 of 24 patients with stage III and IV, respectively. pEFS at 5 years according to stage and completeness of resection is as follows: stage II complete resected 97%; stage II not complete resected 100%; stage III/IV complete resected 92%; stage III/IV not complete resected 63%.(ABSTRACT TRUNCATED AT 250 WORDS)