The Health Council has evaluated the adverse health effects of cyclic acid anhydrides (CAAs) to recommend health-based occupational exposure levels, which specify levels of exposure to airborne substances, at or below which it may be reasonably expected that there is no risk of developing adverse health effects. The primary adverse health effect due to exposure to airborne CAAs is allergic sensitization. No clear threshold level could be found. Alternatively, reference values were calculated: an additional risk of 0.1% due to occupational exposure corresponds to 0.18 µg/m3 for TMA, and 0.007 µg/m3 for HHPA, as an 8-hour time weighted average concentration. Due to insufficient data, no reference values could be determined for other CAAs.