Stress in health care is affected by moral factors. When people are prevented from doing 'good' they may feel that they have not done what they ought to or that they have erred, thus giving rise to a troubled conscience. Empirical studies show that health care personnel sometimes refer to conscience when talking about being in ethically difficult everyday care situations. This study aimed to construct and validate the Stress of Conscience Questionnaire (SCQ), a nine-item instrument for assessing stressful situations and the degree to which they trouble the conscience. The items were based on situations previously documented as causing negative stress for health care workers. Content and face validity were established by expert panels and pilot studies that selected relevant items and modified or excluded ambiguous ones. A convenience sample of 444 health care personnel indicated that the SCQ had acceptable validity and internal consistency (Cronbach's alpha exceeded 0.83 for the overall scale). Explorative factor analysis identified and labelled two factors: 'internal demands' and 'external demands and restrictions'. The findings suggest that the SCQ is a concise and practical instrument for use in various health care contexts.