OnabotulinumtoxinA (onabotA) is approved in the US for 12 therapeutic indications. However, real-world data on the multi-indication use of onabotA are limited, often leading to delayed or reduced treatment. This study provides real-world evidence on the safety of onabotA when treating multiple indications concomitantly. SYNCHRONIZE was a multicenter, retrospective chart-review study evaluating the safety of onabotA for adults treated for two or more therapeutic indications within a three-month period. The primary outcome was treatment-emergent adverse events (TEAEs) within six months post-treatment. A total of 279 patients were included, with the most common concomitant indications being cervical dystonia and chronic migraine (43.4%). The average three-month cumulative dose for multiple indications was 282.2 U. Most patients (62.4%) had a treatment interval for multiple indications of 24 hours or less. Overall, 28.7% of patients reported one or more TEAEs, with no apparent trends related to TEAEs and dose interval or cumulative dose. Reported TEAEs included urinary tract infections (5.7%), neck pain (5.0%), and headache (4.3%). No patient experienced a lack of effect according to clinical objective measurements. SYNCHRONIZE described the real-world safety of onabotA for patients treated concomitantly for two or more indications within a three-month period. TEAEs were generally consistent with the known safety profiles of individual indications, and no new safety signals were identified.