Thank the Spanish Association of Surgeons and the Endocrine Surgery Section for their support in carrying out this work. Thank the 30 Spanish Endocrine Surgery Units for having collaborated in the realization of this project and for having provided the data.

Authorship: Contribution to study of the Authors: 1) Conception and design: A.R. 2) Acquisition of a subtantial portion of data: A.R., J.R.-P., A.B.-R., J.A.P., P.M, E.M., E.F, M.A.M., J.M., M.D., J.M.B., D.C., M.P.S.E., N.M.T., A.E.R., G.M.F., A.M.C., O.V., F.H., G.R.-M., J.M.R. 3) Analysis and interpretation of data: A.R., J.R.-P., A.B.-R., J.A.P., P.M., E.M., E.F., M.A.M., J.M., M.D., J.M.B., D.C., M.P.S.-E., N.M.T., A.E.-R., G.M.-F., A.M.C., O.V., F.H., G.R.-M., J.M.R. 4) Drafting of the manuscript: A.R. 5) Critical revision of the manuscript for important intellectual content: A.R., J.R.-P., A.B.-R., J.A.P., P.M., E.M., E.F., M.A.M., J.M., M.D., J.M.B., D.C., M.P.S.-E., N.M.T., A.E.-R., G.M.-F., A.M.C., O.V., F.H., G.R.-M., J.M.R. 6) Statistical expertise: A.R., G.R.-M. 7) Obtaining funding for this project or study: A.R. 8) Supervision: A.R. 9) Final approval of the version to be published: A.R., J.R.-P., A.B.-R., J.A.P., P.M., E.M., E.F., M.A.M., J.M., M.D., J.M.B., D.C., M.P.S.-E., N.M.T., A.E.-R., G.M.-F., A.M.C., O.V., F.H., G.R.-M., J.M.R. 10) Agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved: A.R., J.R.-P., A.B.-R., J.A.P., P.M., E.M., E.F., M.A.M., J.M., M.D., J.M.B., D.C., M.P.S.-E., N.M.T., A.E.-R., G.M.-F., A.M.C., O.V., FH., G.R.-M., J.M.R.