To clarify the influence of lifestyle habits on the elevated alanine aminotransferase (ALT) levels deterioration of Japanese patients with chronic hepatitis C virus (HCV) viremia, we investigated the effects of smoking, drinking, and physical labor on the disease course of the residents living in a rural area of Kyushu, Japan. The data of patients with chronic HCV viremia and control subjects without HCV infection were analyzed retrospectively from 1986 to 1992 and prospectively from 1993 to 2000. In 2000, a questionnaire was given to 268 HCV-infected patients and 275 control subjects to survey for the lifestyle habits. The data of serial ALT level testing during the observation period was used as a measure of liver damage: 183 HCV patients (68.3%) and 10 control subjects (3.6%) had abnormal ALT levels greater than 35 IU/1 for more than half of their observation period. The percentage of HCV patients with elevated ALT levels significantly increased with the daily consumption of alcohol (p < 0.0001), the length of time spent in strenuous physical labor per day (p = 0.0056), and the number of cigarettes smoked per day (p = 0.0003). A stepwise logistic regression analysis showed male sex (p = 0.003), platelet counts (p < 0.001), strenuous physical labor (p = 0.002), and drinking history (p = 0.007) to be significantly associated with the elevated ALT levels of HCV patients. When strenuous physical labor was done for over 2 h, the probability of elevated ALT levels was increased compared with patients engaging in strenuous physical labor under 2 h (estimated odds ratio = 1.82 [under 2 h], 20.60 [over 2 h]). Interestingly, strenuous physical labor was extracted before alcohol consumption as a significant factor in the elevated ALT levels. Among the control subjects, only the amount of alcohol consumed per day (p = 0.0001) was significantly associated with the elevated levels. These data suggests that strenuous physical labor over a long period of time might be related to elevated ALT levels in patients with chronic HCV viremia as well as drinking.