Scoring systems provide a means for comparing results, ensuring consistent standards and evaluating changes in therapy. The APACHE II system depends partly on the results of laboratory tests which are not normally available in Central Africa. The aim of this study was to develop a scoring system based only on clinical observations. Six hundred and twenty-four consecutive admissions to the intensive care unit (ICU) were allocated a clinical sickness score (CSS) according to pulse rate, blood pressure, respiration rate, urine output, Glasgow Coma Scale, temperature and age. CSS was significantly associated with outcome, there being no significant difference between actual and predicted outcomes calculated by logistic regression analysis. There was a significant difference between mean scores for survivors and non-survivors in all diagnostic groups except diabetes. The proportional change in score from admission was also significantly associated with outcome on each subsequent day in ICU. The CSS provides an objective measure of illness severity for critically ill patients in Africa.