Background: Over the past decades, nursing in Portugal has evolved greatly both academically and professionally and this evolution brought along growing concerns about the quality of the healthcare provided. Due to lack of time or poor organization of the workload, nurses are often faced with the need to choose between what must be done and what will have to be postponed or even not be done at all. Objective: To investigate the care activities that are most frequently left undone or are postponed by nurses working in medical and surgical inpatient units in Portugal. Methods: A descriptive, cross-sectional, quantitative study that follows the RN4CAST (Nurse Forecasting in Europe) methodology was carried out from October 2013 to April 2014. A total of 31 hospitals and a random sample of adult medical-surgical units were involved. The data were collected using a socio-demographic questionnaire and a nursing questionnaire that included the identification of the nursing activities of surveillance and direct patient care that were necessary but postponed or not performed by nurses in their most recent shift. Results: A total of 2,235 nurses participated. Almost all participants had a nursing bachelor degree (98.2%). The most frequently left undone or postponed care items were “Educating patients and family” (50.2%) and “Comfort/talk with patients” (50.1%); the least frequently left undone items were “Treatments and procedures” (3.9%) and “Pain management” (5.6%). Nurses in the North and Center regions of the country were the ones who reported less care left undone due to lack of time. Nurses under the age of 40 were those who reported a highest number of activities left undone. Conclusions: Nurses make selective choices about the care activities that are crucial for the patient. Some activities that may not have an immediate impact on the health of the patients are sidelined, although they may have an impact on other important healthcare quality indicators.