OBJECTIVE: To estimate the health service, non-health service and total costs and predictors of costs in individuals with early inflammatory polyarthritis (IP). METHODS: We conducted a prospective longitudinal study over a 6-month period. The participants were a random sample of 133 individuals who had enrolled with the community-based Norfolk Arthritis Register (NOAR) database between 1994 and 1999. The main outcome measures were the mean (per person) 6-month health service cost, non-health-service cost and total cost associated with IP. RESULTS: One hundred and fifteen of the 133 individuals who were recruited into the study completed 6 months of follow-up. The mean 6-month total cost was estimated to be 2800 pounds sterling per person, of which 14% was health service costs and the remainder non-health-service costs. Higher total costs were associated with lower health status and rheumatoid factor positivity. CONCLUSIONS: Early IP has a considerable impact on both the health-care system and, more importantly, society. Non-health-service costs (i.e. costs incurred by the individual with the disease, their family and friends) account for a substantial proportion (86%) of the total costs associated with early IP.