Ten percent of Lyme arthritis (LA) patients have continued synovitis despite antimicrobial therapy. The current study was designed to (1) investigate predictors of prolonged disease and (2) further define natural history of pediatric LA. Medical records of 94 children fulfilling Centers for Disease Control criteria for Lyme disease were reviewed, classified into groups according to duration of synovitis, and SPSS statistical software was used for analysis. Thirty-nine percent required >6 months and 13% required >12 months to resolve LA. Pearson correlation between duration of symptoms of LA pretreatment and duration of synovitis was not significant. When patients were stratified by group, no differences were found for age, antinuclear antibodies positivity, enzyme-linked immunosorbent assay titer, or reactivity of Western blot using parametric and nonparametric tests. Linear and logistic regression showed no predictors of disease duration. One third of pediatric LA patients require >6 months to resolve synovitis. Duration is not associated with delay in treatment, age, or seroreactivity.