The aim of our study was to demonstrate the suitability of urinary cotinine and plasma thiocyanates (SCN − ) as indicators of tobacco smoking and to investigate the correlation among urinary cotinine, plasma and urine SCN − and number of cigarettes smoked per day and smoking topography. The initial study was conducted with 256 individuals: 143 nonsmokers aged 44.20 ± 15.81 years and 113 current smokers aged 38.02 ± 17.49 years. Subjects were classified into smokers or nonsmokers based on a questionnaire. Cotinine levels were measured using the enzymatic colorimetric method and SCN − using selective electrodes. Urinary cotinine and plasma SCN − levels are both significantly higher in smokers than in nonsmokers and correlate well with the number of cigarettes smoked per day. Urinary cotinine was significantly correlated with duration of consumption (F 3−109 = 3.43; p = 0.019; r = 0.9961), and there was a negative correlation between body mass index and urinary cotinine (r = 0.9989, p < 0.05). Urinary cotinine and plasma SCN − levels discriminate between smokers and nonsmokers and increase when smoking exceeds 20 cigarettes/day and duration of consumption exceeds 5 years.