BACKGROUND Long QT syndrome (LQTS) is a genetic heart rhythm disorder that may present with syncope, seizures, or sudden cardiac death. Breath holding spells (BHS) occur in 5% of all children and have been noted in children with LQTS anecdotally. The purpose of this study was to determine the frequency of BHS in children diagnosed with LQTS at ≤5 years of age. METHODS A retrospective review was performed to identify children diagnosed with LQTS who were ≤5 years old at initial presentation to our LQTS clinic from August 1999 to November 2013. The mean length of follow-up was 6.4 ± 2.8 years. The electronic medical records were reviewed for clinical presentation of BHS, as well as LQTS-associated symptoms, diagnostic tests, and treatment. RESULTS The study cohort consisted of 115 children with LQTS (58% male; median age at diagnosis, 11 months [range, birth to 5 years]; mean corrected QT interval (QTc), 478 ± 60 milliseconds). At presentation, 80% of patients were asymptomatic. Genetic testing revealed type 1 LQTS (LQT1) in 48%. Overall, 5 of 115 patients (4.3%) had BHS (2 of 5 [40%] male, mean QTc: 492 ± 14 milliseconds, 4 [80%] with family history of LQTS). BHS were the presenting symptom in 1 of 23 symptomatic patients (4.3%). All BHS occurred in patients with LQT1 (P = .02). CONCLUSIONS Although BHS among children with LQTS are relatively rare and occur at similar frequency as the general population, they can be the presenting symptom for a heart rhythm disorder. Careful attention to BHS is important to distinguish an innocent BHS from a potential LQTS-triggered cardiac event so that proper treatment is initiated.