Background The length of hospital stay (LOS) for acute pulmonary embolism (PE) varies considerably. Whether the upfront use of a PE prognostic assessment and management pathway is effective in reducing the LOS remains unknown. Methods We conducted a randomised controlled trial of adults hospitalised for acute PE: patients were assigned either to a prognostic assessment and management pathway involving risk stratification followed by predefined criteria for mobilisation and discharge (intervention group) or to usual care (control group). The primary end-point was LOS. The secondary end-points were the cost of prognostic tests and of hospitalisation, and 30-day clinical outcomes. Results Of 500 patients who underwent randomisation, 498 were included in the modified intention-to-treat analysis. The median LOS was 4.0 days (interquartile range (IQR) 3.7–4.2 days) in the intervention group and 6.1 days (IQR 5.7–6.5 days) in the control group (p<0.001). The mean total cost of prognostic tests was EUR 174.76 in the intervention group, compared with EUR 233.12 in the control group (mean difference EUR −58.37, 95% CI EUR −84.34 to −32.40). The mean total hospitalisation cost per patient was EUR 2085.66 in the intervention group, compared with EUR 3232.97 in the control group (mean difference EUR −1147.31, 95% CI EUR −1414.97 to −879.65). No significant differences were observed in 30-day readmission (4.0% versus 4.8%), all-cause mortality (2.4% versus 2.0%) or PE-related mortality (0.8% versus 1.2%) rates. Conclusions The use of a prognostic assessment and management pathway was effective in reducing the LOS for acute PE.