Summary Of 462 Finnhorses (age 1–20 years) evaluated and graded (scale 0–5) radiographically for ossification of the collateral cartilages of the 3rd phalanx of the front feet, 22.9% were totally free from sidebones (Grade 0), and 49.1% had minimal or mild ossification (Grade 1 or 2) at the base of 1 or more of the cartilages. Moderate ossification (Grade 3) was present in 10.2% of the horses, whereas ossification was advanced (Grade 4) or extensive (Grade 5) in 17.8%. In most horses >1 cartilage was affected and 7.6% of the horses had separate centres of ossification in 1 or more of the cartilages. Large sidebones and separate centres of ossification were more common in females than in males (P<0.001). The incidence of large sidebones was lower in young females (1–3 years) than in mares 4–6 years of age (P<0.05), but did not increase significantly with age when young horses, 4–6 years of age, were compared with older ones. Grade 4 and 5 sidebones as well as separate centres of ossification were more common in the lateral than in the medial cartilage (P<0.001), but no difference was observed in this respect between the front feet.