Investigators in Spain retrospectively identified youth and adolescents who started an INI-based regimen between January 1, 2007 and November 30, 2019 to describe clinical outcomes related to INI exposure as well as development of INI-associated drug resistance mutations among those who experienced virological failure.  Data on 318 INI exposures involving 288 individuals (7.3% of whom were ARV naïve at time of INI initiation) were analyzed.  Almost 88% of patients had perinatally-acquired HIV, with prior receipt of several lines of treatment.  48.9% had viremia at INI initiation and 51% were switched onto INI-based therapy from a suppressive regimen.  Dolutegravir was the most frequently prescribed (42.1%), followed by raltegravir (34.6%), elvitegravir (23.0%), and bictegravir (0.3%).  Across the follow-up period (median: 2 years), investigators observed a notable reduction in VL for patients with viremia.  Slightly over half of patients were suppressed at the start of INI-based therapy: this proportion increased significantly to 83.7% at 6 months and 87.4% after 1 year.  Among 27 patients experiencing virological failure, sequences were available for 15 and 7 had major INI mutations; 5/7 had been receiving raltegravir-based therapy and 2/7 were on elvitegravir/cobicistat.  Of 5 patients experiencing virologic failure on dolutegravir, resistance information was not available for 2 and in another 2 no INI drug resistance mutations were detected.