Background Double-checking medications is a widely used strategy to enhance safe medication administration in oncology, but there is little evidence to support its effectiveness. The proliferated use of double-checking may be explained by positive attitudes towards checking among nurses. This study investigated oncology nurses’ beliefs towards double-checking medication, its relation to beliefs about safety and the influence of nurses’ level of experience and proximity to clinical care. Methods This was a survey of all oncology nurses in three Swiss hospitals. The questionnaire contained 41 items on 6 domains. Responses were recorded using a 7-point Likert scale. Multiple regression analysis was used to identify factors linked to strong beliefs in the effectiveness of double-checking. Results Overall, 274 (70%) out of 389 nurses responded (91% female, mean age 37 (standard deviation = 10)). Nurses reported very strong beliefs in the effectiveness and utility of double-checking. They were also confident about their own performance in double-checking. Nurses widely believed that double checking produced safety (e.g., 86% believed errors of individuals could be intercepted with double-checks). In contrast, some limitations of double-checking were also recognized, e.g., 33% of nurses reported that double checking caused frequent interruptions and 28% reported that double-checking was done superficially in their unit. Regression analysis revealed that beliefs in effectiveness of double-checking were mainly associated with beliefs in safety production (p < 0.001). Nurses with experience in barcode scanning held less strong beliefs in effectiveness of double-checking (p = 0.006). In contrast to our expectations, there were no differences in beliefs between any professional sub-groups. Conclusion The widespread and strong believe in the effectiveness of double-checking is linked to beliefs about safety production and co-exists with acknowledgement of the major disadvantages of double-checking by humans. These results are important factors to consider when any existing procedures are adapted or new checking procedures are implemented. Electronic supplementary material The online version of this article (10.1186/s12913-018-2937-9) contains supplementary material, which is available to authorized users.