Acute abdominal pain is the presenting manifestation in approximately 30% of all patients with Willms' tumor. In a small proportion of these patients this pain is significant enough to engender a diagnosis of an acute surgical abdomen. Six of 38 patients with Wilms' tumors treated between the years 1965 and 1975 at the Shands Teaching Hospital of the University of Florida Medical Center have had significant pain. Our experience with these patients emphasizes the importance of thoroughly palpating the abdomen of any child with a suspected acute surgical condition, following induction of anesthesia and prior to initiating the operation. In the absence of any evidence of an acute surgical problem at the time of the exploratory laparotomy, it is also imperative that a careful intra-abdominal examination be performed to exclude the presence of conditions, such as Wilms tumor of the kidney, that may occasionally present in this manner.