Background.Fluoroquinolones (FQs) have been infrequently used in children, largely because of concern that these agents can cause lesions of the cartilage in juvenile animals. However, the relevance of this laboratory observation to children treated with FQs is unknown. A retrospective, observational study was conducted to assess the incidence and relative risk of tendon or joint disorders (TJDs) that occur after use of selected FQs compared with azithromycin (AZ), a drug with no known effect on cartilage or tendons in humans or animals.Methods.An automated database was searched to identify patients younger than 19 years who had been prescribed ofloxacin (OFX), levofloxacin, ciprofloxacin (CPX), or AZ. Potential cases of TJD occurring within 60 days of a prescription of one of the study drugs were identified based on assignment of a claims diagnosis consistent with a TJD within this period. Verified cases were identified by a blinded review of abstracts of medical records from subjects identified as potential cases.Results.The incidence of verified TJD was 0.82% for OFX (13 of 1593) and CPX (37 of 4531) and was 0.78% for AZ (118 of 15 073). The relative risk of TJD for OFX and CPX compared with AZ was 1.04 (95% confidence interval, 0.55 to 1.84) and 1.04 (95% confidence interval, 0.72 to 1.51), respectively. The distributions of claims diagnoses and time to onset of TJD were comparable for all groups. The most frequently reported category of TJD involved the joint followed by tendon, cartilage and gait disorder.Conclusions.In this observational study involving more than 6000 FQ-treated children, the incidence of TJD associated with selected FQ use in children was <1% and was comparable with that of the reference group, children treated with AZ.