Introduction: The mental workload is the set of psychophysical requirements the worker is under throughout his/her working day. If high and long-standing, it can lead to staff fatigue. This represents a risk both for the nurse and for the patients under his/her care. Objective: To analyze the mental workload in nurses who work in different units of a hospital in Bogotá, Colombia. Methods: Quantitative study of descriptive type. For the collection of sociodemographic and occupational information from healthcare nurses, an instrument proposed by the authors was applied, while the tasks evaluation was carried out using the instrument NASA-TLX. Results: The tasks that generate mental workload were administration of the medication (with a score of 58.20), and managerial tasks (54.90). Internal medicine presented serious mental workload (68.15). The morning shift presented serious mental workload (69.61). Conclusions: The most evaluated dimension was time-related demand. The tasks that most generate mental load are administration of the medication, managerial tasks, patient and family education, laboratory tests analysis, and attention code blue.