To document the characteristics and incidence of serious abnormalities in patients prior to admission to intensive care units. Prospective follow-up study of all patients admitted to intensive care in three acute-care hospitals. The study population totalled 551 patients admitted to intensive care: 90 from the general ward, 239 from operating rooms (OR) and 222 from the Emergency Department (ED). Patients from the general wards had greater severity of illness (APACHE II median 21) than those from the OR (15) or ED (19). A greater percentage of patients from the general wards (47.6%) died than from OR (19.3%) and ED (31.5%). Patients from the general wards had a greater number of serious antecedents before admission to intensive care 43 (72%) than those from OR 150 (64.4%) or ED 126 (61.8%). Of the 551 patients 62 had antecedents during the period 8-48 h before admission to intensive care, and 53 had antecedents both within 8 and 48 h before their admission. The most common antecedents during the 8 h before admission were hypotension (n=199), tachycardia (n=73), tachypnoea (n=64), and sudden change in level of consciousness (n=42). Concern was expressed in the clinical notes by attending staff in 70% of patients admitted from the general wards. In over 60% of patients admitted to intensive care potentially life-threatening abnormalities were documented during the 8 h before their admission. This may represent a patient population who could benefit from improved resuscitation and care at an earlier stage.