Life-threatening attacks of asthma requiring intensive care unit (ICU) management at Red Cross War Memorial Children's Hospital in Cape Town were noted to occur in some patients in the same or adjacent months of different years. A retrospective case-controlled study was performed of 21 such 'seasonal' patients who presented to the ICU over a 14-year period. The group made up 6.5% of all asthma patients admitted to the ICU and their 65 admissions made up 15.6% of all ICU asthma admissions during this period. The control group consisted of patients with recurrent admissions that occurred in 'random' months. The two groups were compared in respect of demographic and clinical data. Patients requiring seasonal admissions were shown to form a distinct sub-population of children with severe asthma, some with a family history of fatal asthma, who were less likely to 'outgrow' asthma in childhood, were more likely to require maintenance steroid therapy for asthma management, and significantly more often had positive radioallergosorbent tests to Aspergillus and Cladosporium sp. and to grass pollen. A retrospective analysis of dates of severe asthma attacks may identify individual seasonality, which is a risk factor for life-threatening and intractable asthma.