Ulnar nerve entrapment is the second most common compression neuropathy of the upper extremity. It has been associated with smoking in cross-sectional studies. Our aim was to study whether smoking is associated with ulnar nerve entrapment. The study population consisted of the Northern Finland Birth Cohort 1966 participants, who attended the 31-year follow-up in 1997 (N = 8,716). Information on smoking, body mass index (BMI), long-term illnesses, and socio-economic status were recorded at baseline in 1997. Data on hospitalizations due to ulnar nerve entrapment neuropathies was obtained from the Care Register for Health Care, 1997-2016. Hazard ratios (HR) with 95% confidence intervals (CI) and population attributable risk (PAR) were calculated adjusted for gender, BMI and socio-economic status. 66 patients were diagnosed with ulnar nerve entrapment in the follow-up 1997-2016. Before the age of 31 years, smoking ≤10 pack years associated with more than doubled (HR = 2.57, 95% CI = 1.29-5.15) and smoking >10 pack years with more than five-folded (HR = 5.61, 95% CI = 2.80-11.23) risk for ulnar nerve entrapment compared to non-smokers in the adjusted analyses. Adjusted PAR for smoking (reference of no smoking) was 53.6%. In our study, smoking associated with increased risk for ulnar nerve entrapment, accounting for considerable proportion of increased risk.