PURPOSE: The evaluation of nursing workload is a common practice in intensive care units (ICUs). It allows the calculation of an optimal nurse/patient ratio (N/P) which is a major challenge to ensuring the quality of care while controlling the costs of health care. The objectives of this study were, therefore, to evaluate the N/P ratio and to study nursing activities in intensive care in French-speaking Belgium. METHODS: The Nursing Activities Score (NAS) was prospectively recorded by shift for two periods of one month each in 16 French-speaking Belgian hospitals for a total of 316 ICU beds in 24 ICUs. RESULTS: We included 3377 patients in the study, of which 64% were medical (versus surgical). The results for 24-hour NAS (68.6%) were significantly different from the NAS per shift (Morning: 61.3%, Afternoon: 58.4%, Night: 55.0%). Outliers were significantly more prevalent among men and patients who died and outliers had longer stays in the ICU. Finally, mobilization-positioning and clinical-administrative tasks took, on average, more time for nurses in the ICU. CONCLUSIONS: There is a significant difference in N/P ratio between the Belgian regulation (1/3) and the one calculated by the NAS (1/1.5). A systematic objective assessment of shift workload should be done to avoid N/P ratio differences in intensive care.