Chronic Achilles tendinosis is a condition with unknown aetiology and pathogenesis, most often, but not always, associated with painful nodular thickening of the tendon. In this investigation, 28 tendons (21 patients) with a painful nodule located at the 2-6 cm level in the tendon, and 20 normal (pain-free) tendons, were examined with grey-scale ultrasonography combined with colour Doppler examination. In all tendons with a painful nodule, but not in any of the normal pain-free tendons, neovascularisation was seen in the area with tendon changes (localised widening of the tendon with focal hypo-echoic areas). In tendons with advanced changes, vessels were seen through the entire widened part of the tendons, and both arterial and venous blood flows were registered. The neovascularisation found in this investigation might have implications on the pathogenesis of chronic Achilles tendinosis.