Acute intermittent porphyria is a genetic hepatic porphyria characterized by acute gastrointestinal and neurological symptoms, and accompanied by excess excretion of delta-aminolevulinic acid and porphobilinogen. Here, we report a case of acute intermittent porphyria with attacks of abdominal pain, an elevated serum thyroxine level, and hypercholesterolemia with an increased level of high-density lipoprotein-cholesterol concentration. The diagnosis of acute intermittent porphyria was confirmed by a high urinary excretion of porphobilinogen and a low level of erythrocyte hydroxymethylbilane synthase activity. After being treated with a high carbohydrate intake and propranolol, the patient improved gradually during the following 3 weeks. The patient remained asymptomatic during the 6-month follow-up period. The serum thyroxin and cholesterol levels returned to normal 6 months later. In conclusion, we suggest that for any patient who presents with unexplained abdominal pain, abnormal thyroid function and hypercholesterolemia, a simple Watson-Schwartz urine test should be performed for the screening of acute intermittent porphyria. If the Watson-Schwartz test is positive, the erythrocyte hydroxymethylbilane synthase activity should be determined to confirm the diagnosis of acute intermittent porphyria.