OBJECTIVES: Myotonic dystrophy type 1 (DM1) is a multi-systemic disease affecting skeletal and smooth muscle, the eye, brain, and heart. No disease-modifying therapies are available. Prior studies on clinical care and economic burden combined DM1 and DM type 2. This study describes the US DM1 population aged ≥12 years, assessed organ system involvement over time, estimated healthcare resource utilization (HCRU), associated costs, and identified predictors of high-cost status. METHODS: Linked open claims and EHR data (Clarivate) from 1 January 2015 to 25 August 2023 were analyzed. Eligible individuals had a DM1 diagnosis (index), ≥6 months pre-index data, and were aged ≥12 years; congenital DM was excluded. Organ system involvement rates up to 7 years post-index were estimated using the Kaplan-Meier method. Annual HCRU rates and costs to payers (2023 USD) were summarized by setting, type of care and specialty and compared by organ involvement. Predictors of high-cost status were evaluated using multivariable logistic regression. RESULTS: The cohort included 1,343 people with DM1. Over 7 years, most experienced neurological, gastrointestinal, cardiac, pulmonary, and/or musculoskeletal system involvement. Annually post-index, approximately 24% of patients had emergency room visits, and 15% had inpatient visits. Common specialty visits included rehabilitation (13%), cardiology (13%), and neurology (11%). Frequent device use included noninvasive positive-pressure ventilation (12%), assistive devices (7%), and oxygen therapy (4%). Mean annual total cost of care was $20,687 (SD = $122,082), primarily driven by inpatient and outpatient hospital visits. Cardiac and pulmonary complications were significant predictors of high-cost status. CONCLUSION: DM1 imposes significant clinical and economic burden, marked by extensive organ involvement and variable healthcare costs. As any patient may progress to costly cardiac or pulmonary complications, early proactive management is critical. The complexity and heterogeneity of DM1 highlight ongoing unmet needs and the importance of developing effective treatments.