A study was undertaken to establish the ranges of prostate dimensions, weight and volume in mature normal dogs and thus provide information which would allow differentiation from normality of size changes associated with disease. The study was performed on 154 healthy adult male entire dogs. Each prostate was imaged ultrasonographically and standard longitudinal and transverse sections were obtained. Prostate length (L), depth on longitudinal (DL) and transverse sections (DT) and width (Wr were measured. Prostatic volume and weight were estimated according to formulae derived previously. There were statistically significant correlations between bodyweight or age and L, DL, DT and W, There were also significant correlations between estimated prostatic weight or volume and bodyweight, age, L, DL, DT and W, Formulae wen! derived to express the relationships between prostate size (weight or volume) and age or bodyweight.