Abstract. This work is an acoustic investigation on some spectral and temporal characteristics of the speech of patients with recurrent paralyses, and also of patients without diagnosed paralyses but with alteration of their voice after thyroid surgery. Speech is evaluated during two tasks: producing sustained vowels and also a sequence of nonsense words. Consequences of surgery on the voice of patients are evaluated in order to identify the different perturbations that such a surgery may provoke, and also to uncover probable compensatory or readjustment strategies which a patient might deploy, alone or with the help of speech therapy. Globally, results show that due to surgery, some aspects of the speech production system are perturbed, as highlighted by the spatial and temporal parameters measured. However, these parameters tend to become normal as the patient recovers, in time and with the help of speech therapy. This is a longitudinal study.