A prospective case-controlled study was conducted in order to determine the transmission route of community-acquired hepatitis C virus (HCV) infection in Taiwan. Thirty-eight consecutive patients (25 men and 13 women) with acute community-acquired HCV infection and 76 age (within 3 years)- and sex-matched healthy control subjects without HCV infection were enrolled. Serum anti-HCV was tested by second generation immunoassay. The sera of 26 family members from 12 families of index patients were also tested for anti-HCV. A questionnaire covering the history of blood transfusion, surgery, intravenous drug abuse, prostitute contact, dental procedures, injection, acupuncture, tattooing, and ear-piercing was conducted among patients and control subjects. Univariate analysis revealed injection with nondisposable needles was an independent risk factor (P = 0.02, odds ratio = 4.17, 95% confidence interval = 1.24-14.47) associated with HCV infection. Other risk factors were not significant. Only 2 (7.7%) family members of index patients had an anti-HCV. In conclusion, more vigorous effort to prohibit the use of nondisposable needles should be promoted to interrupt the spread of community-acquired HCV infection in Taiwan. Of note, a significant number of patients (34.2%) contracted HCV infection without identifiable risk factors. Unidentified routes need to be investigated.