Since its introduction in 1985, Kt/V urea has played a pivotal role as a marker of “dialysis adequacy”. Over the decades, multiple clinical practice guidelines have adopted and subsequently relaxed Kt/V targets, which were then transformed into quality metrics in various healthcare systems, including the United States. In this perspective, we explore the historical origins of Kt/V, focusing on its adaptation to peritoneal dialysis (PD). We critically examine literature linking Kt/V to patient outcomes and explore the limitations of Kt/V—including reliance on urea removal alone as a surrogate for the clearance of all uremic toxins, the flawed assumption of equivalence between residual kidney and dialytic urea clearances, and the challenges in estimating the volume of distribution of urea.