Low-rate smoking patterns are common, but their pulmonary effects remain poorly known. The study hypothesis was that any level of daily smoking may cause chronic obstructive pulmonary disease (COPD). We investigated the association between longitudinal smoking patterns and COPD using logistic regressions and survival models adjusted for multiple covariates. Data from Finnish Twin Cohort surveys were used. Participants (n = 21,609) were grouped into categories describing 1981 smoking and change in smoking during 1975-1981. Light smoking was defined as