Autoimmune hypothyroidism is a common medical condition. Its revelation by thyrotrophic hyperplasia is an unusual and may be misdiagnosed as a pituitary adenoma. A 35-year-old man is referred to us for endocrinological assessment before surgery of a pituitary macroadenoma with bitemporal hemianopsia. Biological data reveal profound primary hypothyroidism. With thyroid hormone substitution, the thyroid function was normalized. Follow-up magnetic resonance imaging, showed the complete shrinkage of the pituitary mass attesting of a thyrotrophic pituitary hyperplasia. This case highlights the importance of a multidisciplinary assessment of pituitary masses to avoid unnecessary surgery and to prevent consequences of sellar masses.