Objective To investigate the relationship between pre-symptom onset live births and functional outcome in women with inflammatory polyarthritis (IP). Methods 1872 women with no subsequent pregnancies were registered with the Norfolk Arthritis Register between 1990 and 2004 and followed-up for a median of 5 years. Functional disability over time was assessed by Health Assessment Questionnaire (HAQ). The number and calendar year of past live births were recorded. Differences in HAQ score over time by parity and time since last live birth (latency), adjusted for age and symptom duration, were examined using linear random effects models. The results were then adjusted for a number of potential confounders. Results 1553 women (83%) had =1 live births before symptom onset. The median latency was 26 years (IQR 16–35). Parous women had significantly lower HAQ scores over time than nulliparous women (-0.19, 95% CI -0.32 to -0.06). Increasing latency was associated with increasing HAQ score; the mean HAQ score of women with a latency of approximately 32 years was the same as for nulliparous women. This was independent of autoantibody status, socioeconomic status, smoking history and comorbidity. Conclusion Parous women who develop IP have better functional outcome over time than nulliparous women who develop IP. The beneficial effect of parity diminishes with time.