Prisons worldwide operate under crowded conditions, in which prisoners are forced to share a cell. Few studies have looked at the relationship between cell sharing and the quality of prison life in Europe. This study aims to fill this gap with a multilevel analysis on the link between cell sharing and quality of prison life, using results from a Dutch prisoner survey. Findings show that cell sharing is associated with lower perceived prison quality, which is partially mediated by reduced quality of staff–prisoner relationships. Cell sharing thus undermines the Dutch penological philosophy, which considers staff–prisoner relationships to be at the heart of prisoner treatment and rehabilitation. It is recommended that prisoners are held in single rather than double cells.