Although hypo- and hyperthyroid patients have different symptoms in the gastrointestinal tract, the mechanism of thyroid action on the gut remains poorly understood. Thus the aim of this study was to investigate the effect of hypo- and hyperthyroidism on gastric myoelectrical activity, gastric emptying, dyspeptic symptoms. Twenty-two hyperthyroid (median age 45, 15 females) and 11 hypothyroid (median age 42, 10 females) patients were included into the study. Dyspepsia score, hypo- and hyperthyroid symptom scale, abdominal ultrasonography and upper gastrointestinal endoscopy were performed. Gastric myoelectrical activity was measured by electrogastrograpy ( EGG) before and after therapy both preprandially and postprandially and compared with age, gender, and body-matched controls (12 for hypothyroid, 15 for hyperthyroid patients). Radionuclide gastric emptying studies were performed with a solid meal. Hypothyroid patients revealed a significant increase in preprandial tachygastria as compared with controls (12.3% vs 4.8%). The percentage of preprandial normal slow waves (2.4-3.7 cpm) was below 70% (dysmotility) in 7 of 11 hypothyroid patients versus 2 of 12 controls (P < 0.05). Hyperthyroid patients revealed a significantly higher preprandial (3.1 vs 2.8) and postprandial (3.4 vs 3) DF when compared with the controls (P < 0.05). A higher percentage of postprandial taschygastria (7.9 vs 0) was present in hyperthyroid patients than in the controls (P < 0.05). The decrease on postprandial EGG power (power ratio < 1) was observed in 7 patients the in hyperthyroid group and 1 in controls (P < 0.05). The percentage of postprandial normal slow waves was below 70% in 10 of 20 hyperthyroid patients vs 1 of 15 controls (P < 0.05). After therapy these differences disappeared in the euthyroid state. The hypo- and hyperthyroid symptom scale correlated to dyspepsia score. Dyspepsia score in hyperthyroidism correlated to power ratios in hyperthyroid patients. We detected some correlations between serum levels of fT3 or fT4 and some EGG parameters in hypo- and hyperthyroidism. Dyspepsia score and hypo- and hyperthyroid symptom scale were improved significantly after therapy in the euthyroid state. In conclusions, we showed gastric dysrhythmia by EGG in both hypo- and hyperthyroid patients. Dyspeptic symptoms correlated to the activity of thyroid disease. After therapy, these findings and dyspeptic symptoms improved in the euthyroid state. Abnormalities of power ratios may be responsible of dyspeptic symptoms in hyperthyroid patients. EGG may be a useful and noninvasive tool for detecting gastric disturbances during hypo- and hyperthyroidism.