In captivity colobine monkeys often display a soft to watery faecal consistency, in contrast to their wild conspecifics, which usually display well-formed faeces. It has been suggested that dietary fibre, and possibly also dietary water content is related to faecal consistency. To further test this assumption we pooled data on 15 individual feeding periods from six feeding trials with colobine monkeys from different species, during which dietary and faecal chemical composition had been determined and faeces consistency had been scored with one consistent scoring scheme. Our pooled data suggest that dietary neutral detergent fibre (NDF) and dietary dry matter content were significantly, positively correlated to a better faeces consistency, whereas dietary protein content was negatively correlated to faeces consistency. Influences on the faeces consistency like easy digestible carbohydrates and the mineral content of the diet were not considered. Firmer faeces did not contain less water, but more NDF and less protein. It is suggested that diets fed to colobine monkeys in Dutch zoos should be reduced in protein and dietary water, and increased in fibre content. A recognized problem for attaining this goal is the lack of a readily accepted primate pellet that is not only called “high fibre” but that actually mimics the fibre content of the diet of free-ranging colobine monkeys.