Most patients with cystic fibrosis (CF) present with respiratory or digestive symptoms. About 3% of patients have electrolyte disturbances at the time of diagnosis, but most of the described cases presenting with this manifestation have been in children. Only 3 adult patients are identified in the literature who first presented with hypokalemia. We describe a morbidly obese African American adult who presented with severe hypokalemia and metabolic alkalosis, which eventually led to the diagnosis of CF after multiple hospitalizations over 4 consecutive summers. Besides being the first African American adult with this presentation, he had the highest BMI, lowest serum potassium, highest pH, and highest bicarbonate level. In the summer of 2015, a 26 year-old African American man presented to the hospital for generalized weakness. His BMI was 54 kg/M2, and he had been on a special diet for a few months with a weight loss of 50 pounds. He sweated profusely while working as a chef. Laboratory tests showed severe hypokalemia and metabolic alkalosis. Further work-up pointed toward extrarenal losses of potassium. He was treated with intravenous normal saline and potassium chloride. After discharge, his potassium level remained normal through the winter while the potassium was tapered off. However, over the following three summers, he repeatedly presented to hospitals for the same problems. Cystic fibrosis was suspected and confirmed by an abnormal pilocarpine sweat test. Gene test revealed two mutations of cystic fibrosis transmembrane conductance regulator (CFTR). Thereafter, his potassium level remained normal with potassium replacement during summertime. Unexpectedly, however, his BMI rose to 83 kg/M2 after he stopped the special diet for weight reduction. The reason for the delayed diagnosis is discussed. We present an exceedingly rare case of CF in a morbidly obese African American adult male whose only manifestation of CF was hypokalemia and metabolic alkalosis. Clinicians should keep an open mind to the diagnosis of CF in ethnically diverse populations, even if it seems unlikely at first glance. For "summer hypokalemia", consider cystic fibrosis.