Background and objective Incident, adverse event (AE) and complaint data are typically used separately, but may be related at the patient level with one event triggering a cascade of events, ultimately resulting in a complaint. This study examined relations between incidents, AEs and complaints that co-occurred in admissions. Methods Independently and routinely collected incident, AE and complaint data were retrospectively linked for surgical admissions in an academic centre (2008-2014). Two investigators reviewed whether incidents/AEs in admissions were clinically related and in what sequence (incident preceding vs following AE). Likelihood of occurrence of AEs and AE cascades (ie, ≥3 AEs) was studied using logistic regression analyses. Results Complaints were filed for 33 (0.1%) of 26 383 admissions. Complaints filed by patients with incidents and/or AEs (n=13) mostly addressed quality/safety problems, whereas other complaints mostly addressed relationship problems. Incidents and AEs co-occurred in 730 (2.8%) admissions, which seemed clinically related in 34% of these cases. Incidents with related AEs preceded as well as followed AEs (56.6%/44.4%). Patients with incidents were at greater risk of AEs than patients without incidents, even for seemingly unrelated AEs (OR 1.4; 95% CI 1.3 to 1.6). Risk of AE cascades was greater when patients with AEs also had incidents, regardless of whether these seemed related (unrelated: OR 2.0; 95% CI 1.6 to 2.5; related: OR 5.7; 95% CI 4.3 to 7.4) or whether incidents preceded or followed AEs in these admissions (53% vs 52%, P>0.05). Conclusions Patient-level linkage of incident, AE and complaint data can reveal relations between events that otherwise remain obscured, such as incidents that trigger as well as follow AEs, introducing event cascades, regardless of whether clinical relations seem present.@en