To determine whether the Cigarette Dependence Scale, the Fagerström Test for Nicotine Dependence, and the Nicotine Dependence Syndrome Scale (NDSS) reliably and correctly assessed both weakly and severely dependent individuals, the authors collected data via Internet from 2,435 current smokers, from 2004 to 2007. They used a 2-parameter item response model to determine the difficulty and discrimination of each question and used correlations between latent scores to assess convergent and discriminant validity. The reliability of all scales was close to or exceeded.70. Both the Cigarette Dependence Scale and the Fagerström Test for Nicotine Dependence had 1 misfitting item. Each NDSS scale had at least 2 misfitting items. The information curve of each of the questionnaires peaked between -2 and 2 and was low at both extremes. All questionnaires had adequate reliability and were more informative for a medium level of the underlying cigarette dependence continuum than for both extremes of this continuum. The correlations between latent scores indicated good convergent validity between questionnaires and low discriminant validity between NDSS subscales, except for Tolerance. This result suggests that nicotine dependence may not be composed of 5 dimensions but may be unidimensional and distinct from reduced sensitivity to the effects of smoking (Tolerance).