Abstract Despite international guidelines, it is common practice in many European countries for prisoners to share a cell. In many cases this may be a measure to cope with overcrowding, but in the Netherlands it is a policy measure to reduce costs and flexibly adjust capacity. While the harms of overcrowding are widely recognised, less is known about the effects of cell sharing in non-overcrowded conditions. This study considers the association between cell sharing, wellbeing, misconduct, and prison climate, using data from a national survey study among Dutch prisoners (N = 3408). Findings show that cell sharing is associated with poorer ratings of wellbeing and prison climate, especially for people who prefer a single cell. Prisoners in double cells who do not get along with their cellmate report more misconduct. These findings reinforce recommendations to house people in single cells, unless they prefer otherwise.