Lead exposure is a common public health problem. Exposure to the metal can cause hematological, gastrointestinal, rheumatological, endocrine, neurological and renal problems in humans. However, effects on the thyroid gland are controversial. We retrospectively investigated thyroid function parameters in 65 adult males who had been occupationally exposed to lead. We then compared the findings with those of 60 male patients who had no history of lead exposure or thyroid abnormalities, who served as the control group. The mean ages of the lead-exposed workers and the controls were 34.3 ± 7.9 and 32.9 ± 6.6 years respectively. Blood lead levels in the lead-exposed workers were significantly higher than in the control group. The lead-exposed workers were assigned to one of three groups according to their blood lead levels, as follows: 40–59 μg/dl, 60–79 μg/dl, or 80 μg/dl and above. Thyroid Stimulating Hormone (TSH) levels in the 80 μg/dl and above group were significantly higher than in either the 40–59 μg/dl group or the 60–79 μg/dl group. However, TSH levels in the 40–59 μg/dl group did not differ significantly from those in the 60–79 μg/dl group. These results suggest that high levels of lead in the blood may affect thyroid physiology. Clinicians should be aware of the potential hazardous effects of lead on the thyroid, especially in patients who have been occupationally exposed to lead.