Quality healthcare should be grounded on clinical practice with the highest benefit-risk ratio and cost-effectiveness according to the available scientific evidence. The overuse of unproven diagnostic or therapeutic procedures is common in our setting and leads to increased healthcare spending and even iatrogenic harm. Previous cost-effectiveness initiatives have proposed identifying diagnostic and therapeutic measures that are better 'not done' in certain clinical contexts under the lens of the available scientific evidence. In this regard, the Spanish Society of Endocrinology and Nutrition (SEEN) has compiled a series of 'not-to-do' recommendations from its various working groups. These recommendations cover common clinical situations classified into the following thematic areas: diabetes, nutrition, pituitary gland, neuroendocrine tumors, thyroid, and hormone replacement therapy in postmenopausal women.