Background: Measuring the circumference of the abdomen is still commonly used when treating a patient with suspicion of intra-abdominal bleeding. In the present study the usefulness of this method for a diagnostic purpose is questioned because of the assumed method-related interindividual variation. Methods: The study group consisted of 34 end-stage renal failure (ERSF) patients treated with peritoneal dialysis. Each patient was measured by the same nurse at the level of the umbilicus and the level of the iliac crest both before and after an infusion of 2000 ml of peritoneal dialysis fluid into the peritoneal cavity. One healthy female served as a control. Her abdominal circumference was measured at the level of the umbilicus by 10 different emergency medical technicians (EMTs), each of whom performed the measurement three times. The measuring tape was blank and the place of the first measurement was marked as performed in clinical practice. Results: The mean abdominal circumference at the level of the umbilicus before an infusion of peritoneal fluid was 93.2 ± 9.5 cm (SD), and after filling the peritoneal cavity 96.3 ± 9.5 cm (difference 3.1 ± 1.7 cm). These figures at the level of the iliac crest were 96 ± 8.3 and 97.2 ± 8.4 cm (difference 1.2 ± 1.4 cm) (P < 0.0001), respectively. The mean value between the smallest and largest values when measuring the circumference of a healthy control person was 1.85 ± 1.11 (P < 0.0005). The mean difference in circumference in the peritoneal dialysis patients was smaller than the largest difference among the three measurements taken by the same EMT. Conclusion: Measuring the abdominal circumference should not be used as a diagnostic tool when intra-abdominal bleeding is suspected.