Spinal muscular atrophy type 1 (SMA1) is a rare, rapidly progressing, debilitating, genetic neuromuscular disease. The first treatment for SMA1, nusinersen, was recently FDA-approved (12/23/2016). As the treatment landscape evolves, an updated assessment of the burden of SMA1 is warranted. This study assessed the healthcare resource use (HRU) and costs among patients with SMA1 in real-world practice. In this retrospective claims analysis, patients with SMA1 were identified from Symphony Health's Integrated Dataverse® (09/01/2016–08/31/2018). The index date was the first SMA1 diagnosis date after 12/23/2016 and the study period spanned from the index date until death or end of available data. HRU and costs per-patient-per-year (PPPY; 2018USD) were described during the study period for all patients and following treatment initiation for the subset of patients treated with nusinersen. A total of 349 patients with SMA1 were included; median age was 1 year old and 55.6% were females. Over a median follow-up of 7.9 months, the proportion of patients receiving mechanical ventilation, nutritional support, and physical therapy/rehabilitation was 46.4%, 46.1%, and 22.6%, respectively. Patients had, on average, 59.4 days with medical visits per year (14.1 inpatient days), 13.4 of which were related to respiratory failure. Among the 45 patients initiated on nusinersen, patients had, on average, 56.6 days with medical visits per year following treatment initiation (4.6 inpatient days), 11.4 of which were related to respiratory failure. Excluding nusinersen-related costs, mean healthcare costs PPPY were $137,627 (median: $43,167) among all patients and $92,618 (median: $29,425) among the subset of patients treated with nusinersen. In addition, mean nusinersen-related costs were $191,909 (median: $144,487) per month for the first 3 months post-initiation (i.e., loading phase) and $36,882 (median: $16,132) per month thereafter (i.e., maintenance phase). HRU and costs associated with SMA1 are substantial, even among patients treated with nusinersen.