OBJECTIVES: The objective of this study was to evaluate to what extent pain severity was associated with impairment of regular daily activities other than paid work. METHODS: Study data originated from a prospective, non-interventional study of people with NP treated with the capsaicin patch QUTENZATM. Repeated observations from baseline- and 12-week follow-up assessments for the Numerical Pain Rating Scale (NPRS) ‘average pain in the last 24 hours’ score, and the Activity Impairment (AI) score from the Work Productivity Activity Index (WPAI-NP) were analysed. The NPRS subjectively records pain on a scale between 0 (no pain ) and 10 (worst imaginable pain). The WPAI-NP Activity Impairment Index measured the extent to which NP affected regular daily activities from 0% (no effect) to 100% (complete prevention). Generalized linear mixed models (GLMM; SPSS v20), with a normal probability distribution, identity link function, and a first-order autoregressive covariance structure were tested to determine the relationship between WPAI-NP-AI (scale) and NPRS (ordinal).  RESULTS: 171 patients with NP contributed 253 combined observations from baseline and week 12 follow-up assessment. Mean age at baseline was 59.4 years (sd 14.9) and 44% of subjects were male. The GLMM model that best fitted the data (smallest information criterion) had one random effect (subject+intercept) and two fixed effects (Sex+NPRS+intercept). The significant (p<0.05) fixed-effects coefficients were: (Intercept) 14.2+(Male: β -7.0; 95%CI -13.5,-0.5)+(NPRS3: 24.4;9.0,39.8)+(NPRS4:9.4;13.5,45.3)+(NPRS5:36.5;21.2,51.8)+(NPRS6:43.7;28.5,60.0)+(NPRS7: 46.3;31.1,61.5)+(NPRS8: 58.5;42.6,74.4)+(NPRS9:2.0;44.2,79.8)+(NPRS10:72.2;54.7,89.7). The estimated marginal mean WPAI-NP-AI increased linearly from 10.1% at NPRS 0 to 84.8% at NPRS 10. Predicted WPAI-NP-AI was highly correlated with observed values (R-squared=0.889); mean absolute error (predicted-observed) was 9.6 (sd 6.9). CONCLUSIONS: In people with chronic NP, increasing pain severity was associated with a linear increase in impairment of regular daily activities other than paid work. Interventions that reduce pain are likely to improve functioning.