Abstract Background Preoperative portal vein embolization (PVE) is performed in patients with insufficient future remnant liver (FRL) to allow safe resection. Although many studies have demonstrated an increase in FRL volume after PVE, little is known about the increase in FRL function. This study evaluated the increase in FRL function after PVE using 99mTc-labelled mebrofenin hepatobiliary scintigraphy (HBS) with single photon emission computed tomography (SPECT) and compared this with the increase in FRL volume. Methods In 24 patients, computed tomography volumetry and 99mTc-labelled mebrofenin HBS with SPECT were performed before and 3–4 weeks after PVE to measure FRL volume, standardized FRL and FRL function. A hypothetical model was used to assess safe resectability after PVE. The limit for safe resection for FRL function was set at an uptake of 2·69 per cent per min per m2. For FRL volume and standardized FRL, 25 or 40 per cent of total liver volume was used, depending on the presence of underlying liver disease. Results After PVE, FRL function increased significantly more than FRL volume. The correlation between the increase in FRL volume and FRL function was poor. Using the hypothetical model, seven patients did not achieve a sufficient increase in FRL function to allow safe resection 3–4 weeks after PVE, compared with 12 and nine patients based on FRL volume and standardized FRL respectively. Conclusion The increase in FRL function after PVE is more pronounced than the increase in FRL volume, suggesting that the necessary waiting time until resection may be shorter than indicated by volumetric parameters.