Excessive usage of the Internet can negatively affect health and health practices especially among youth. To examine the issue among Turkish students, this study determined the association between high-school students' attitudes towards Internet usage and their health behaviour. The sample (n = 2043) was randomly drawn from all students at two high schools in Turkey: one in Anatolia and one (a vocational school) in Istanbul. Data were collected using the Structured Questionnaire, Attitude Scale towards Internet Usage (ASTIU) and Adolescent Lifestyle Profile (ALP). The mean age of the students was 16.3 years, 77.7% were male and 96.9% used the Internet; mean duration of Internet use was 18.8 h/week. Female students had more positive attitudes towards Internet usage. Mean scores for ASTIU and ALP were 72.58 (SD 17.64) and 111.34 (SD 16.61) respectively, which were average levels. There was a statistically significant but weak overall negative correlation between adolescents' attitudes towards Internet usage and their health behaviour. Our results concur with studies in different cultures which suggest some negative effects, of heavy Internet use.