The diagnosis of cystic fibrosis (CF) generally is made within the first few years of life, although some cases will not be diagnosed until adulthood. For most patients the diagnosis is suggested by typical CF-related symptoms such as chronic respiratory infection or maldigestion. The authors describe an adult patient with newly diagnosed CF whose presenting abnormalities consisted of hypokalemia and metabolic alkalosis. These are known complications of CF but are not common presenting features that lead to the diagnosis of CF. The authors discuss their patient's presentation and review his metabolic manifestations of CF.