The aim of this study was to determine which of the following factors--size of the post-excisional defect, site of the defect and type of reconstruction--influence tongue mobility and articulation disorders after treatment for cancer of the tongue and floor of the mouth. A total of 60 patients, who had been evaluated at least 6 months after surgery followed by radiotherapy (60 Gy in 30 fractions), were evaluated. According to the size of the post-excisional defect patients were divided into two groups: (1) defect less than 5 cm (35); (2) defect more than 5 cm (25). Based on the localisation of the defect patients were also divided into two groups: (1) anterior tongue and/or floor of the mouth (30); (2) lateral tongue and/or floor of the mouth (25) and tongue base (5). According to the type of reconstruction patients were divided into three groups: partly reconstructed (18); reconstructed with locally available tissue--local flaps (27); and with pectoralis major myocutaneous (PMMC) flaps (15). Articulation proficiency was assessed through Articulation Test and tongue mobility through Tongue Mobility Test. According to results of this study, type of reconstruction followed by size of post-excisional defect seemed to be the most influential factor in tongue mobility and articulation disorders after the tongue and floor of the mouth cancer treatment. Site of the defect has no influence.