When patients with aggressive lymphoma present with intraabdominal disease, a stable residual mass is frequently detected radiographically at the time of the clinical complete remission. To discern the optimal management for this clinical problem, we reviewed 241 patients with aggressive lymphoma treated at the National Cancer Institute (NCI) from 1977 to 1986. Seventy-two/241 patients (30%) had an abdominal mass at diagnosis and 29/72 (40%) were left with a radiographically detectable residual mass at clinical complete remission. The likelihood of a residual mass was much higher for patients with bulky disease (P2 less than .0003) (two-tailed test P2). Twenty-nine patients had radiologically stable residual masses after therapy, and of 22 (76%) with pathologic evaluations, 21 had negative specimens (95%) and one was positive (5%). None of the patients with negative pathologic evaluation has relapsed in the abdominal site (median follow-up, 31 months). Seven patients were observed clinically without laparotomy: five are alive, without evidence of disease, at 2 to 9 years; two relapsed with disseminated disease within 2 months of chemotherapy. Initial tumor size and size of the residual mass did not correlate with residual disease, since residual masses identified by radiographic examination did not usually harbor viable lymphoma cells. Aspiration cytology was negative for residual tumor in 15/16 cases. One negative result was not confirmed at laparotomy, presumably due to sampling error. The one positive aspiration was followed by a negative laparotomy, possibly due to subsequent tumor necrosis. Restaging laparotomy has a low yield. In most patients with aggressive lymphoma who have otherwise completely responded to carefully administered full-dose combination chemotherapy, stable residual abdominal masses can be closely followed clinically without surgical exploration.