BACKGROUND The TEMPO 3:4 Trial results suggested that tolvaptan had no effect compared with placebo on albuminuria in autosomal-dominant polycystic kidney disease (ADPKD) patients. However, the use of categorical 'albuminuria events' may have resulted in a loss of sensitivity to detect changes. The aim of this study is to investigate the effects of tolvaptan on albuminuria as a continuous variable. METHODS Post hoc analysis of a 3-year prospective, blinded randomized controlled trial, including 1375 ADPKD patients. Albuminuria was measured in a spot morning urine sample prior to tolvaptan dosing and expressed as albumin-to-creatinine ratio (ACR). RESULTS Baseline median (interquartile range) ACR was 3.2 (1.7-7.1) mg/mmol. Of note, 47.9% of ADPKD patients had normal, 48.7% moderately increased and 3.4% severely increased ACR. Subjects with higher baseline ACR had higher blood pressure and total kidney volume (TKV) and lower estimated glomerular filtration rate (eGFR). During follow-up, higher baseline ACR was associated with more rapid eGFR loss (P < 0.0001 for trend), but not with rate of growth in TKV. During the 3-year trial, ACR rose in placebo- and decreased in tolvaptan-treated patients (+0.23 versus -0.40 mg/mmol). The difference ACR increased over time, reaching a maximum of 24% at Month 36 (P < 0.001). At that time only a minor difference in blood pressure was observed (mean arterial pressure -1.9 mmHg for tolvaptan). The decrease in ACR was similar in all subgroups investigated, and remained after withdrawal of study drug. The beneficial effect of tolvaptan on TKV growth and eGFR loss was stronger in patients with higher baseline ACR. CONCLUSIONS In ADPKD, higher baseline albuminuria was associated with more eGFR loss. Tolvaptan decreased albuminuria compared with placebo, independent of blood pressure. Treatment efficacy of tolvaptan on changes in TKV and eGFR was more readily detected in patients with higher albuminuria.