The public health burden of arthritis and related conditions is incompletely described by commonly used public health surveillance systems. We examined the potential of administrative data as a supplement. The administrative data sources we used underestimated the prevalence of arthritis and overestimated service utilization for persons with arthritis when data from only one year were used. The use of five year's data doubled the prevalence estimate and reduced the service utilization estimate by half. The demographics of the population covered by administrative data also influence the prevalence estimate. Administrative data may usefully supplement routine public health surveillance systems but must be used with caution.