Hypovolemic shock is not an uncommon presentation in nephrotic syndrome, yet it is seldom mentioned in the literature. This study was performed to investigate the prevalence of hypovolemia and hypovolemic shock in the acute nephrotic stage, and the association of hemoconcentration and abdominal pain with hypovolemic status. Two hundred and twenty-five patients with a total of 328 admissions to the pediatric ward of our hospital during 1983 to 1996 were retrospectively reviewed for hypovolemic episodes. Clinical presentation and laboratory data including hemoglobin, serum sodium, albumin, cholesterol, and triglyceride levels were investigated. Thirteen patients with 19 episodes (5.8%) of hypovolemic shock were found, and had more severe hemoconcentration (hemoglobin 19.6 +/- 2.2 g/dL) and hyponatremia (127.3 +/- 7.2 mEq/L). Another 33 patients with 41 symptomatic hypovolemic episodes without hypotension (12.5%) were found, and their hemoglobin levels were higher compared to patients without hypovolemic symptoms. Among 61 episodes of abdominal pain and hemoconcentration, 58 were responsive to albumin infusion. This suggested the presence of hypovolemia. Twenty patients had abdominal pain without hemoconcentration, and 18 of them had primary peritonitis. Hypovolemia was found in patients at the acute nephrotic stage, and was usually associated with hemoconcentration and abdominal pain. A combined examination of hemoglobin and serum sodium is the best indicator of hypovolemic status. Both primary peritonitis and hypovolemic episodes should be taken into consideration when managing abdominal pain in children with nephrotic syndrome.