We report on the development of a new assessment tool to monitor recovery after severe traumatic brain injury (TBI). Although a number of scales exist to identify such recovery, most are limited if one is interested in monitoring small changes or in setting goals for rehabilitation. This is due to the fact that items are too broad, they may cross more than one dimension (e.g. cognition and motor functioning) and there is a danger that recording of responses may be too subjective. The Wessex Head Injury Matrix (WHIM) was developed to avoid these problems. We observed 88 people with severe TBI. These were consecutive admissions to two hospitals. Mean coma duration was 14 days and mean duration of post traumatic amnesia (PTA) was 56 days. Of 145 behaviours observed, we selected 62 and each behaviour was compared to every other behaviour to determine a likely order of recovery. The resulting WHIM is an observational tool to assess and monitor cognitive recovery after severe head injury. It can be used with patients who are in coma, just out of coma or who are minimally conscious. Two case examples are provided.