Purpose Although it is well known that acromegaly causes enlargement in the extremities, studies investigating the effects of acromegaly on tendons, muscles and soft tissue are limited. The aims of our study were to investigate tendons, the presence of enthesitis, soft tissue, muscle groups in terms of thickness and pennation angle (PA) which is an indicator of microstructure and strength of the muscle, of the lower extremities. Methods Thirty-nine patients with acromegaly and thirty-nine healthy control subjects similar for age, sex and body mass index were enrolled. Lower extremity tendons, skin, muscle groups were evaluated by ultrasound. Results The thicknesses of heel skin, heel pad, plantar fascia and Achilles tendon were higher in acromegaly than the control group (p < 0.05). The incidence of Achilles enthesitis were increased in the acromegaly group (p < 0.05). The thicknesses of the gastrocnemius medial head, vastus medialis, lateralis muscles for both sides and the left rectus femoris muscle were found to be lower in the acromegaly patients than controls (p < 0.05). However, thicknesses of vastus intermedius, gastrocnemius lateral head and soleus were similar between the acromegaly and control groups (p > 0.05). PA values of the right and left vastus medialis and the right vastus lateralis were found to be decreased in the acromegaly group (p < 0.05). Myostatin levels were lower in acromegaly group (p < 0.05). Conclusions Acromegaly may cause to an increase in tendon and soft tissue thickness, enthesitis formation, decrease in the thickness of some muscles, and deterioration in microstructures in lower extremity.