Aims: Thyroid dysfunction is a known finding in alcoholism. Most studies have reported the reduction in peripheral thyroid hormones in acute withdrawal and long-term abstinence periods of alcohol dependence. The aim of the present study was to investigate the alterations of free thyroid hormones in early and late withdrawal and their association with aggression, age of onset, and family history of alcoholism. Methods: Male inpatients (n = 39; mean age +/- SD: 42.55 +/- 8.02 years) in alcohol withdrawal were compared with healthy men (n = 28; mean age +/- SD: 38.31 +/- 9.26 years). Levels of free thyroxine (fT4), free triiodothyronine, (fT3) and thyrothrophin (TSH) were measured in early (first day) and late (28th day) withdrawal in the patients and only once in the controls. Results: In early withdrawal, levels of thyroid hormones did not differ from those in the controls. In late withdrawal, fT3 and fT4 levels (2.71 +/- 0.56 and 10.80 +/- 1.86 pg/ml) were lower than those of both controls (3.32 +/- 0.41 and 11.95 +/- 1.49 pg/ml, respectively, P < 0.05 in both cases) and patients in early withdrawal (3.18 +/- 0.72 and 12.68 +/- 2.50 pg/ml, respectively, P < 0.05 in both cases). Patients were divided into subgroups according to aggression level, onset age of alcoholism, and family history. While the high-aggression group had lower serum levels of fT3 and fT4 in late withdrawal (2.49 +/- 0.41 and 10.44 +/- 2.15 pg/ml) compared with those of controls (P < 0.05 in both cases), the low-aggression group only had lower serum levels of fT3 in late withdrawal (2.90 +/- 0.62 pg/ml) compared with those of controls (P < 0.05). fT3 and fT4 values in the family history-negative group (2.67 +/- 0.56 and 10.75 +/- 1.88 pg/ml) were lower than those of controls in late withdrawal (P < 0.05 in both cases). Both fT3 and fT4 levels in late withdrawal (2.69 +/- 0.54 and 10.83 +/- 1.96 pg/ml) were decreased in early-onset group compared with those of controls (P < 0.05 in both cases). Conclusion: Decreased free thyroid hormone levels may be a result of heavy alcohol consumption or a trait marker of alcoholism, especially in high-aggressive, early-onset and family history-negative patients.