Researchers report that sirolimus is “unsafe and ineffective” in patients with autosomal dominant polycystic kidney disease (ADPKD) and renal insufficiency. Ruggenenti et al. compared the efficacy of sirolimus plus conventional therapy versus conventional therapy alone in 41 patients with ADPKD and chronic kidney disease stage 3b or 4. At 1 year follow-up, total kidney volume had increased by 9.0% in the sirolimus group compared with 4.3% in the control group; glomerular filtration rate decreased significantly in both groups. Moreover, albuminuria and proteinuria increased significantly and two patients developed end-stage renal disease in the sirolimus group. Early termination of the trial was recommended for safety reasons.