The share of California’s workers’ compensation claims identified as cumulative traumas (CT) nearly doubled between 2018 and 2025, with the sharpest growth occurring after 2021, according to a new California Workers’ Compensation Institute (CWCI) study. The study found that the increase was widespread, extending beyond regions and industries that historically accounted for the largest share of CT claims, but traditional factors such as population and employment growth, overall claim volume and changes in worker tenure explain relatively little of the increase, raising questions about what is driving the continued growth of CT claims.

The study uses data from CWCI’s Industry Research Information System (IRIS) to examine CT claim trends statewide and evaluate factors that may help explain the increase. It found that CT claims rose from about 1 in 11 California workers’ compensation claims in 2018 to 1 in 6 in 2025, with most of the increase coming after the first two years of the COVID-19 pandemic. Other key findings from the study include:

• Growth was widespread. CT rates increased across every region, industry, body-part category and worker-tenure group examined. Los Angeles continued to have the highest CT rate, but some of the largest increases were in regions where CT claims historically were less common, including the Bay Area and Central Valley.
• CT claims became less geographically concentrated. CT claim volume in the Central Valley increased 136% between 2018 and 2025, while in the Inland Empire/Orange County region it increased 98%. Los Angeles, despite having the highest CT rate in both years, had the smallest increase in CT claim volume at 25%.
• Traditional workforce factors explain little of the growth. CT claims increased in regions with both expanding and contracting labor markets. Population and employment trends, declining overall claim volume and changes in worker tenure did not account for a significant share of the statewide increase.
• Multiple filings contributed to the growth but more workers filing CTs was the primary driver. 87% of the increase in the CT rate analyzed at the individual-worker level was attributable to more workers filing at least one CT claim; 13% was associated with an increase in the average number of CT claims per worker.
• The types of body-part claims shifted. While rising CT rates within body-part categories accounted for most of the increase, the mix of claims shifted toward categories with relatively high CT rates. The largest increases were in Soft Tissue, Other Facial Soft Tissue and Mental Disorder claims.
• Applicant attorney representation shifted geographically. Southern California applicant attorneys increasingly represented claimants in CT cases involving Northern California employers, with their share increasing from 23% in 2019 to 79% in 2025. This expansion coincided with the widespread adoption of remote and virtual hearings during the pandemic, which reduced practical barriers to representing workers and litigating cases across the state. At the same time, the share of CT cases involving Northern California employers that were filed in Southern California venues increased from 15% to 38%.

The study identifies several areas for future research, including how the geographic expansion of applicant attorney representation, changes in law firm concentration, and attorney business practices may be related to the growth of CT claims. CWCI says further analysis of these factors will help stakeholders better understand the evolving CT litigation landscape in California.

Overall, the study documents a substantial, widespread increase in CT claims that cannot be fully explained by population and employment growth, overall claim frequency, or changes in workforce composition, suggesting that broader structural changes within the system merit closer examination as CT claims continue to grow.

CWCI’s has published its study as a Report to the Industry, California Cumulative Trauma Claims: 2018–2025: Trends and Factors Associated with Growth. It is available for free at www.cwci.org.

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CWCI found that California workers' comp cumulative trauma claim growth was widespread but uneven, suggesting that no single industry, region, or workforce characteristic fully explains the statewide increase.