ObjectiveTo provide new evidence on how tonsils surgery in children has geographically varied over time in the context of the Spanish National Health System.DesignObservational ecological spatiotemporal study on geographical variations in medical practice, using linked administrative datasets, including virtually all surgeries performed from 2003 to 2015.SettingThe Spanish National Health System, a quasi-federal structure with 17 autonomous communities (ACs), and 203 healthcare areas (HCAs).ParticipantsPatients aged 19 and younger residing in the HCAs and ACs.InterventionsTonsillectomy with adenoidectomy (T&A); and tonsillectomies alone (T).Main endpoints(1) Evolution of T&A and T rates; (2) spatiotemporal variation in the risk of receiving T&A or T surgery at regional level (ACs) and HCAs; and (3) the fraction of the variation (FV) attributed to each of the components of variation—ACs, HCAs, year and interaction ACs year.ResultsT&A age-sex standardised rates increased over the period of analysis from 15.2 to 20.9 (5.7 points per 10 000 inhabitants). T alone remained relatively lower than T&A rates, evolving from 3.6 in 2003 to 3.9 in 2015 (0.3 points per 10 000 inhabitants). Most of the risk variation was captured at the HCAs level in both procedures (FV: 55.3% in T&A and 72.5% in T). The ACs level explained 27.6% of the FV in the risk in T&A versus 8% in T. The interaction ACs year was similar in both procedures (FV: 15.5% in T&A and 17.5% in T). The average trend hardly explained 1.46% and 1.83% of the variation, respectively.ConclusionOur study showed wide persistent variations with a steady increase in rates and risk of T&A and a stagnation of T alone, where most of the variation risk was explained at HCA level.