There is very little recent investigative work on the contribution of health related impairment and disability to either accident risks or to reduced performance at sea, the only exception being studies on fatigue and parallel data on sleep related incidents. Incidents where health related impairment, other than fatigue, has contributed are very rarely found in reports of maritime accident investigations. This may either indicate the irrelevance of these forms of impairment to accidents or alternatively point to the effectiveness of existing control measures. The main approach to risk reduction is by the application of fitness criteria to seafarers during medical examinations. Where there is a knowledge base it is either, as in the case of vision, a very old one that relates to patterns of visual task that differ markedly from those in modern shipping or, as with hearing, is based on untested assumptions about the levels of impairment that will prevent effective communications at sea. There are practical limitations to the assessment of cognitive functions as these encompass such a wide range of impairments from those associated with fatigue, medication, or substance abuse to those relating to age or to the risks of sudden incapacitation from a pre-existing illness. Physical capability can be assessed but only in limited ways in the course of a medical examination. In the absence of clear evidence of accident risks associated with health-related impairments or disabilities it is unlikely that there will be pressure to update criteria that appear to be providing satisfactory protection. As capability is related to the tasks performed, investigations need to integrate information on ergonomic and organizational aspects with that on health and impairment. Criteria that may select seafarers with health- -related impairment need to be reviewed wherever the task demands in modern shipping have changed, in order to relax or modify them where indicated in order to reduce unjustifiable discrimination.