Background and objectives: Symptoms due to slowing of gastrointestinal motility constitute an important problem in most patients with primary hypothyroidism. The purpose of this study was to calculate gastric emptying time in patients with primary hypothyroidism using a radioisotopic method. Patients and methods: Fifteen hypothyroid patients (2 male, 13 female) participated in the study. Mean age was 43 (range 38-50) years. Only patients who had been recently diagnosed and had received no previous therapy were included in the study. Radiological and endoscopic examination of the upper gastrointestinal tract was carried out. Patients with gastric outlet obstruction were excluded. Twelve healthy and euthyroid people with no detectable gastrointestinal pathology were examined as a control group. The mean age of this group was 45 (range 35-55) years. Patients and control group received a semisolid meal containing 1 mCi technetium-99m sulphur colloid and measurements were made from the epigastrium. Results: Mean gastric emptying half-time (t(half)) was 112.13 ± 48.96 min in hypothyroid patients and 57.87 ± 6.38 min in the control group. Gastric emptying time of the hypothyroid patients was significantly different from the control group (P < 0.001). There was no correlation between gastric emptying time and serum thyroid-stimulating hormone (TSH) levels. Conclusion: We concluded that radioisotopic study is a safe, rapid and reliable method for determining gastric emptying time in patients with primary hypothyroidism.