The aim of the study was to adapt and validate the perceived implicit rationing of nursing care instrument in the Slovak nurse work environment and to evaluate the prevalence of unfinished nursing care in acute care hospitals.The measurement of unfinished nursing care could be assumed as a proxy indicator of nurse staffing adequacy or higher risk of adverse events.A cross-sectional survey design was used. The sample of 1,429 registered nurses from 21 hospitals in Slovakia was recruited. Exploratory factor analysis, confirmatory factor analysis and internal reliability were performed.The instrument is essentially rather an inventory than scale per se. Concurrent validity of the Slovak version was supported by the significant associations between unfinished nursing care and clinically relevant variables.The prevalence of unfinished nursing care based the percentage of positive responses was higher than prevalence based on composite mean scores. Findings from the study raise questions about a unidimensional structure of nursing tasks reflected in most commonly used survey instruments of unfinished nursing care internationally.The periodical measurement of unfinished nursing care based on the percentage of positive responses should be assumed as a key strategy to increase patient safety and quality of nursing care.