INTRODUCTION: Mirror movements (MM) are involuntary shudders which occur at the same time as voluntary movements of the homologous contralateral muscles. They may occur alone or associated with other pathology. CLINICAL CASES: We present three new cases of congenital MM (CMM) and discuss their clinical, physiopathological and genetic aspects. Case 1. A four year old boy was brought to the clinic because he dropped things held in one hand when he tried to take things with the other. On examination it was seen that when he made a voluntary movement with one hand, the other hand made a similar movement simultaneously and involuntarily. This phenomenon had been observed since he was a few months old. Apart from this, the rest of the neurological examination was normal. Cerebral MR was also normal. Neuropsychological assessment showed borderline intellectual function. Case 2. The first patient's father, who was 26 years old, knew no details of his own family history. Since childhood he had noticed that he himself had made similar movements to those of his son. However, with time, he had managed to partially control and even inhibit these movements. His cerebral MR scan was normal. Case 3. An 11 year old boy consulted for MM, non-fluctuating congenital palpebral ptosis and nocturnal enuresis. The neurological examination and his intelligence were found to be normal. One of his sisters had palpebral ptosis and nocturnal enuresis without MM. His cerebral MR, X-ray of his spine, EMG, electroretinogram, CPK, blood lactate, glucemia, urine and urological examination were normal. CONCLUSIONS: MM may be another manifestation within the clinical spectrum of diverse encephalopathies; may be associated with different syndromes (Kallman, Klippel-Feil and Usher amongst others) or may present alone. Both familial and sporadic cases have been described. We consider our cases 1 and 2 to be of the familial CMM condition, with autosomal dominant inheritance, in which MM was the only finding. The association observed in case 3 has not previously been described. It may possibly be a condition transmitted by autosomal recessive inheritance.