Giant basal cell carcinoma(BCC) is a clinical expression of a large-sized BCC, which can cause extensive local invasion and disfigurement and have a particular capacity for metastasis. In the development of this large tumor, several risk factors including patient neglect, aggressive histological features and long duration, are identified. We have observed a very large BCC on the forehead of anlderly man for more than 4 years. He had been suffering from psychiatric disease for a long time, and patient neglect due to this problem played a crucial role in the development of this giant BCC.