For decades Parkinson's disease has been considered to be limited to disturbed motor functions and its association with a cognitive deterioration is very recent. The frequency of cognitive decline varies according to the authors between 3% and 93% depending on the different criteria of evaluation. Owing to the discrepancy among the previous studies our object has been to determine the existence of cognitive changes of statistical significance, since even nowadays the relation between neuropsychology and physiopathology has been misunderstood. A total of 50 patients between 52 and 85 years old with Parkinson's disease have been neurological and neuropsychologically evaluated and the results correlated with 50 healthy controls. Patients, who presented clinical signs of demence according to the criteria of DSM III or any other neurological or general disease were excluded because of possible side effects on the motor cognitive phase. For the neuropsychological study Signoret's Battery of Cognitive Efficiency test (BEC 96) was used, it evaluates: the attention, orientation, thinking, memory, recognition, serial learning, fluency, naming and constructional functions. It was observed that all the patients with Parkinson's disease performed these tests worse than the controls, except for attention. From the statistical point of view the differences are highly significant (p < 0.001) for serial learning and constructional tests and significant (p < 0.05) for orientation, thinking fluency and naming. In the area of mnesic functions the patients with Parkinson's disease show an alteration that predominates significantly on serial learning, however, it is less important for logical memory. All the alterations correspond to the long term memory.(ABSTRACT TRUNCATED AT 250 WORDS)