Background. The adult acquired flat foot is caused by a complete or partial tear of the tibialis posterior tendon. We present the results of flexor digitorum longus transfer and medializing calcaneal osteotomy for recontruction of the deformity. Material & Methods. Twenty-six patients (31 feet) with an average age of 58 years (36–75) were operated for an acquired flat foot deformity. The patients were seen before surgery, one year after surgery and an average of 85 months after surgery to assess the following parameters: AOFAS Score, VAS Score for pain (0–10). Foot x-rays in full weightbearing position (dorsoplantar and lateral) were done at every visit in order to assess the following parameters: tarsometatarsale angle on the dorsoplantar and lateral x-ray, talocalcaneal angle on the lateral x-ray, calcaneal pitch angle and medial cuneiforme height on the lateral x-ray. Results. The AOFAS hindfoot score improved from 46.4 to 89.5 (max.: 100) points 1 year postoperatively und decreased to 87.8 points at the last follow-up. VAS for pain decreased from 6.6 to 1.1 at the one year follow-up and increased to 1.5 at the last follow-up. All radiologic parameters improved and stayed without significant changes over time. Following complications were seen: one recurrence, two patients with irritation of the sural nerve, one patient with hypesthesia of the big toe. In six patients the screws had to be removed. Apart from that no other revision surgery had to be done. Conclusion. Flexor digitorum longus transfer together with medializing calcaneal osteotomy provides excellent results for the therapy of acquired flat foot deformity. The results did not change significantly over time