Smoking is a leading cause of preventable death, causing approximately five million premature deaths world-wide each year1, 2. Evidence for genetic influence on smoking behaviour and nicotine dependence (ND)3-8 has prompted a search for susceptibility genes. Furthermore, assessing the impact of sequence variants on smoking-related diseases is important for public health reasons9, 10. Smoking is the major risk factor for lung cancer (LC)11-14, and one of the main risk factors for peripheral arterial disease (PAD)15-17. We have identified a common variant in the nicotinic acetylcholine receptor gene cluster on chromosome 15q24 with an effect on smoking quantity, ND and the risk of two smoking-related diseases in populations of European descent. The variant has an effect on the number of cigarettes smoked per day in 15,771 smokers (P=6×10−20). The same variant associated with ND in a previous genome-wide association study using low quantity smokers as controls (OR=1.3, P=1×10−3)18, 19, and with a similar approach we observe a highly significant association with ND (OR =1.40, P=7×10−15). Comparison of LC (N=1,024) and PAD (N= 2,738) cases with about 30,000 population controls each showed that the variant confers risk of LC (OR=1.31, P=1.5×10−8) and PAD (OR=1.19, P=1.4×10−7). The findings highlight the role of nicotine addiction in the pathogenesis of other serious diseases and provide a case study of the role of active gene-environment correlation20 in the pathogenesis of disease.