Background: Since 1996 adverse events (AE) in therapeutic apheresis (TA) have been more extensively registered in Sweden. This report analyzes the extent and relation of AEs to procedures and diagnoses. Materials and methods: Reporting of TA performed in Sweden was centralized. A separate system for the registration of AE in TA was established and the data received were entered into a central database for registration and analyses. Fifteen of all 35 apheresis units reported both TA and AE during 1996-1999. These centers performed 75% of all TA procedures. Adverse events included medical symptoms, vascular access problems, technical and other problems. Results: More than 14,000 procedures were registered during the observation period. No fatalities occurred. AEs occurred in 3.7% (1996), 4.6% (1997), 4.2% (1998) and 4.4% (1999) of procedures. Interventions during the adverse event were performed in about 65% of the events. Apheresis procedures were interrupted due to an adverse event in about 1%. Adverse events occurred in 5.6% of plasma exchanges, 1.9% of plasma modulations and 6.8% of cytapheresis procedures. Paresthesia was registered in 22% and hypotensive events in 20.5%. Other more frequent symptoms were urticaria (14.4%), shivering (7.4%) and nausea (7.4%). AEs were most frequent in patients with Goodpasture's syndrome (12.5%), TTP/HUS (10.5%) and GuillainBarré syndrome (11.0%). Conclusion: AEs are few, often mild and less common in plasma modulation than plasma exchange. AEs are more frequent during TA of patients with certain diagnoses such as TTP/HUS. Copyright © 2001 Elsevier Science Ltd.