A cohort study based on the Swedish Spine Register. To determine the relation between smoking status and disability after surgical treatment for lumbar spinal stenosis. Smoking and nicotine have been shown to inhibit lumbar spinal fusion and promote disc degeneration. No association, however, has previously been found between smoking and outcome after surgery for lumbar spinal stenosis. A large prospective study is therefore needed. All patients with a completed 2-year follow-up in the Swedish Spine Register operated for central lumbar stenosis before October 1, 2006 were included. Logistic regression was used to assess the association between smoking status and outcomes. Of 4555 patients enrolled, 758 (17%) were current smokers at the time of surgery. Smokers had an inferior health-related Quality of Life at baseline. Nevertheless, adjusted for differences in baseline characteristics, the odds ratio (OR) for a smoker to end up dissatisfied at the 2-year follow-up after surgery was 1.79 [95% confidence interval (CI) 1.51-2.12]. Smokers had more regular use of analgesics (OR 1.86; 95% CI 1.55-2.23). Walking ability was less likely to be significantly improved in smokers with an OR of 0.65 (95% CI 0.51-0.82). Smokers had inferior Quality of Life also after taking differences before surgery into account, either when measured with the Oswestry Disability Index (ODI; P < 0.001), EuroQol (P < 0.001) or Short Form (36) Health Survey (SF-36) BP and SF-36 PF (P < 0.001). The differences in results between smokers and nonsmokers were evident, irrespective of whether the decompression was done with or without spinal fusion. Smoking is an important predictor for 2-year results after surgery for lumbar spinal stenosis. Smokers had less improvement after surgery than nonsmokers.