Abstract: Objective To study the clinical characteristics and diagnostic methods of pituitary hyperplasia caused by primary hypothyroidism in order to avoid its misdiagnosis. Methods Sella area occupying lesion, found in 9 patients by X-ray radiograph, CT and MRI, was diagnosed as pituitary hyperplasia caused by primary hypothyroidism, by endocrine function test and bone age examination, and treated with thyroxine replacement therapy. Results The 9 patients were treated with thyroxine replacement therapy and followed up for 4-18months. The endocrine function test was normal except for TSH. The symptoms were improved at different extents. MRI showed that the size of lesion became obviously smaller in 2 patients. Conclusion Since primary hypothyroidism can be easily misdiagnosed as pituitary adenoma, its diagnosis should be established based on endocrine function test and bone age examination and treated with thyroxine replacement therapy.