[ES] Introducci?n: La asociaci?n de patolog?a tiroidea y paratiroidea es frecuente y puede dificultar el diagn?stico preoperatorio por lo que debe hacerse estudio tiroideo funcional y estructural en el hiperparatiroidismo. Objetivo: Conocer la incidencia de patolog?a quir?rgica de paratiroides y tiroides asociadas. Material y m?todo: Estudio hist?rico de casos y control en 105 pacientes sometidos a paratiroidectom?a total o parcial por hiperparatiroidismo primario (83,81%) o secundario (16,19%) con o sin tiroidectom?a (60% y 40% respectivamente) entre enero de 2006 y diciembre de 2013. Como grupo control se seleccionaron aleatoriamente 126 tiroidectom?as realizadas en el mismo periodo excluyendo carcinoma medular de tiroides. Resultados: La incidencia de tiroidectom?a asociada a paratiroidectom?a fue del 60% [50,44-68,86%] sin diferencia significativa entre hiperparatiroidismo primario y secundario. La incidencia de carcinoma tiroideo no medular asociado a paratiroidectom?a fue 7,62% [3,91-14,32%], la de carcinoma tiroideo incidental fue 6,67% [3,27-13,13%] ambos sin diferencia estad?sticamente significativa respecto al grupo control (6,35%, [3,25-12,03%]). Discusi?n: La asociaci?n de gammagraf?a Tc99m-MIBI y ecograf?a incrementa la exactitud del diagn?stico preoperatorio, descarta patolog?a tiroidea asociada y se recomienda como estudio rutinario. La indicaci?n de tiroidectom?a asociada a la paratiroidectom?a debe tomarse preoperatoriamente con id?nticos criterios que en la poblaci?n general y solicitar al paciente consentimiento informado. Conclusiones: Un alto porcentaje de pacientes sometidos a paratiroidectom?a precisan tiroidectom?a por lo que es necesario hacer estudio tiroideo prequir?rgico para establecer la indicaci?n de tiroidectom?a si fuese necesaria y solicitar al paciente consentimiento para realizar tiroidectom?a en todos los casos. [EN] Introduction: The association of thyroid and parathyroid disease is common and may hinder the preoperative diagnosis, this is the reason why a functional and structural thyroid study should be made in hyperparathyroidism. Objective: To determine the incidence of surgical pathology associated thyroid and parathyroid. Material and method: Historical study of 105 cases and control in patients undergoing total or partial parathyroidectomy for primary hyperparathyroidism (83.81%) or secondary (16.19%) with or without thyroidectomy (60% and 40 % respectively) between January 2006 and December 2013. a control group of 126 thyroidectomies performed in the same period excluding medullary thyroid carcinoma were randomly selected. Results: The incidence of thyroidectomy associated with parathyroidectomy was 60% [ from 50.44 to 68.86 %] with no significant difference between primary and secondary hyperparathyroidism. The incidence of non-medullary thyroid carcinoma associated with parathyroidectomy was 7.62% [3.91 to 14.3%] , the incidental thyroid carcinoma was 6.67% [3.27 to 13.13%] with no difference both statistically significant compared to the control group (6.35 % [3.25 to 12.03%]). Discussion: The association of 99mTc -MIBI scintigraphy and ultrasound increases the accuracy of the preoperative diagnosis, rule out thyroid disease associated and is recommended as a routine study. The indication for thyroidectomy associated with parathyroidectomy should be taken preoperatively with the same methods as in general population and obtain informed consent from the patient. Conclusions: A high percentage of patients undergoing parathyroidectomy require thyroidectomy so it is necessary to establish preoperative thyroid study indicating thyroidectomy if necessary and obtain the patient?s consent to perform thyroidectomy in all cases.