Introduction: A squamous cell carcinoma of the oral cavity or mobile tongue represents the sixth most common type of cancer worldwide. Patient work-up procedures vary among institutions, though generally include clinical, imaging, and histopathology examinations. This study had two aims: assess the accuracy of ultrasound (US) and magnetic resonance imaging (MRI) for evaluating tumor thickness of ventral tongue squamous cell carcinoma, and ascertain the effects of biopsy on imaging results. Methods: We retrospectively examined the medical records of 69 patients diagnosed and treated for ventral tongue squamous cell carcinoma stage T1 or T2. We compared tumor thickness in US and MRI results with histological thickness measured using specimens obtained in a partial glossectomy. Results: The mean difference between thickness measured with MRI before the biopsy procedure and that of the pathological specimens was 0.28 mm while that between US imaging results before the biopsy and histologic thickness was 0.75 mm. Furthermore, following the biopsy, the mean difference between thickness shown by MRI and that of the histological specimens was 0.89 mm, and between US findings and histologic thickness was 2.67 mm. There was a positive correlation between thickness shown by MRI and US when performed before the biopsy and the pathological result. Conclusions: MRI and US results appear to have adequate accuracy for estimating the thickness of T1-and T2 lesions of the tongue when scanning is performed prior to a biopsy procedure. Furthermore, the present findings confirm the clinical impression that inflammatory changes induced by a biopsy often alter later imaging findings.