Summary Data on acute chest syndrome (ACS) in adult sickle cell disease patients are scarce. In this study, we describe 105 consecutive ACS episodes in 81 adult patients during a 32‐month period and compare the characteristics as a function of the time to onset after hospital admission for a vaso‐occlusive crisis (VOC), that is early‐onset episodes (time to onset ≤24 h, 42%) versus secondary episodes (>24 h, 58%; median [interquartile range] time to onset: 2 [2–3] days). The median age was 27 [22–34] years, 89% of the patients had an S/S or S/β 0 ‐thalassaemia genotype; 81% of the patients had a history of ACS (median: 3 [2–5] per patient), only 61% were taking a disease‐modifying treatment at the time of the ACS. Fever and chest pain were noted in respectively 54% and 73% of the episodes. Crackles (64%) and bronchial breathing (32%) were the main abnormal auscultatory findings. A positive microbiological test was found for 20% of episodes. Fifty percent of the episodes required a blood transfusion; ICU transfer and mortality rates were respectively 29% and 1%. Secondary and early‐onset forms of ACS did not differ significantly. Disease‐modifying treatments should be revaluated after each ACS episode because the recurrence rate is high.