In Ireland one in four (28%) of those attending hospital emergency departments have substance abuse-related injury/illness and one in eight (13%) present in a state of clinical intoxication. Health care professionals working in emergency departments are frequently exposed to patients with substance use problems and are in ideal positions to provide early diagnosis and treatment. The success rate in detecting these patients is however disturbingly low (25-50%) and as a result many substance use problems are misdiagnosed or remain undetected. International studies that focus on primary care and addiction within the mental health sector suggest that health care professionals' knowledge and attitudes regarding substance use and substance users may negatively influence the care that these patients receive. There is a dearth of empirical research, internationally, and particularly in Ireland that addresses health care professionals' knowledge and attitudes in relation to substance use and substance users with no empirical evidence to ascertain in particular, emergency department doctors' and nurses' knowledge and attitudes.