BACKGROUND: The interplay between smoking, oxidized low-density lipoprotein cholesterol (ox-LDL) and gonadal hormones has been scarcely investigated. AIM: To investigate associations in ox-LDL and gonadal hormones in smokers and non-smokers METHODS: Participants (n=164) were obtained from a population cohort of Finnish men aged 40-70 years. The subjects answered a detailed questionnaire on their health behaviour, medication, diseases, and different symptoms, and the hormonal and lipid profiles were measured. RESULTS: Smokers (n=33) had higher levels of ox-LDL (21%) and more free testosterone (12%) (P<0.01 for all) than non-smokers (n=131). The difference between smokers and non-smokers in ox-LDL persisted after controlling for possible confounding factors. When the smokers were divided into two subgroups (n=16 and n=17) according to total testosterone (< or =15 and >15 nmol/L), the ox-LDL in the low-testosterone subgroup was significantly higher (30%) than in the high-testosterone group (P=0.006). Similarly in the corresponding non-smoking subgroups (n=72 and n=59), ox-LDL was significantly higher (11%) in the low-testosterone subgroup than in the high-testosterone subgroup (P=0.012). CONCLUSIONS: Smoking men have significantly more ox-LDL than non-smoking men. Furthermore, if smoking is combined with a low serum testosterone, ox-LDL is even higher. This may suggest a higher risk for atherosclerosis.