Pilot fatigue has been identified as a determinative factor in various safety events, leading to the introduction of Fatigue Risk Management regulations and standards worldwide. The scope of this study was to examine whether event and pilot characteristics recorded in safety investigation reports were associated with fatigue when the latter was stated as a contributing/causal factor. The sample consisted of 296 reports published by various investigation authorities and referred to safety events occurred between 1990 and 2014. The researchers conducted frequency analyses and Chi-square / Fisher Exact tests as a means to examine possible associations. Flight crew fatigue was found as a cause in 8.8% of the reports and was more frequently present in occurrences during evening and night operations, take-off, climbing, approach and landing phases, and Control Flight into Terrain and Runway Excursion eventualities. No significant differences were found regarding the year of occurrence, aircraft age, weight and type (jet, propeller, rotary), flight type (Commercial Air Transport and other), operation type (passenger and non-passenger) and event severity. Regarding the pilot characteristics, the more the hours on duty the higher the frequency of events where fatigue was recognised as a factor. No association was detected between the frequency of fatigue related events and pilots’ age, hours of experience in the respective aircraft type and in total, and, surprisingly, regarding sleeping and resting hours before reporting for duty. The findings only partially confirmed associations of fatigue with the operational, event, aircraft and flight crew characteristics included in this study, and showed that fatigue had contributed to (serious) incidents and accidents with about the same frequency. The results suggest a consideration of quality of flight crew sleep/rest before reporting on duty.