Rationing of nursing care (RNC) is characterized by the omission of any aspect of the required patient care, resulting in incomplete or delayed nursing activities. Oncology nurses are exposed to a very high psychological burden, which can lead to the development of professional burnout syndrome (PBS). The level of PBS might be related to life and job satisfaction. This study aimed to identify determinants affecting RNC and reveal the relationship between RNC, life and job satisfaction, and the PBS levels among oncology nurses. The sample was a hundred oncology nurses from four hospitals in Poland with a mean age of 43.26 ± 10.69 years. The study was conducted from March 2019 to February 2020. The self-administered sociodemographic questionnaire and validated scales determining missed nursing care, job and life satisfaction, and life orientation were used: Basel Extent of Rationing of Nursing Care—Revised (BERNCA-R), Satisfaction with Job Scale (SWJS), Satisfaction with Life Scale (SWLS), Life Orientation Test-Revised (LOT-R), and Maslach Burnout Inventory (MBI). The mean BERNCA score was 1.55 ± 0.15, which indicates the frequency of RNC was between “never” and “rarely”. The mean SWJS score was 11.71 ± 5.97, which showed that nurses were “dissatisfied” and “rather dissatisfied” with their job. A low SWLS score was reported by 59% of nurses, which means that more than half of the respondents described their life satisfaction as low. In LOT-R, 66% of nurses reported pessimistic and 31% neutral life orientation. The mean overall MBI score was 49.27 ± 19.76 points (EE = 63.56 ± 25.37, DEP = 37.2 ± 24.95, and lack of PA = 47.05 ± 22.04), which means that half of the nurses perceived burnout and half did not. Additionally, the higher the job satisfaction (SWJS), the more frequent the RNC (BERNCA) (p < 0.05). The greater the EE, the stronger the sense of lack of PA, and the higher the PBS (MBI) level, the less frequent the RNC (BERNCA). In conclusion, there is a phenomenon of omission of some aspects of care among oncology nurses, but it is not frequent and concerns areas not directly related to therapeutic tasks, but requiring effort and not resulting in quick noticeable effects. It depends only little on life satisfaction and more on job satisfaction and PBS level. The results may indicate the professionalism of Polish nurses, their responsibility towards their patients’ life and health, and the sense of mission that enables them to perform their duties regardless of the external and internal difficulties. The presence of the PBS phenomenon in oncology nurses highlights the need for continued research in this area.