Between January 1993 and April 1994, 5 patients with cystic fibrosis, aged 4-9 months, were admitted to the Department of Pediatrics, University of Berne, Switzerland, with acute, severe metabolic alkalosis (sodium < 133 mmol/l, plasma potassium < 3.5, chloride < 85, bicarbonate > 35.0 mmol/l, blood pH > 7.43). 87 cases of acute metabolic alkalosis complicating cystic fibrosis reported in the literature between 1951 and 1995 were also reviewed. Our cases and those described in the literature demonstrate that acute metabolic alkalosis occurs in patients aged 2 years or less. Anorexia, vomiting, respiratory exacerbation, fever, and body weight loss often precede metabolic alkalosis. Furthermore, metabolic alkalosis is a common initial presentation of cystic fibrosis, suggesting that this diagnosis should be considered in the context of unexplained metabolic alkalosis.