The clinical and biochemical characteristics of metachromatic leukodystrophy (MLD), true adult forms and late juvenile forms which are still living at adulthood, are reviewed as they both are observed in adult Neurology and Psychiatry departments. Mental deterioration is often the first symptom, evolving progressively; and dementia finally occurs. The latency before the appearance of neurological objective symptoms may be long and extend for several years. In many cases, the behavioral abnormalities are the first symptoms. Some of these forms have been diagnosed as schizophrenia. Very seldom, neurological symptoms, especially ataxia, occur without cognitive or psychiatric disturbances. Most of these cases have pyramidal and cerebellar symptoms, at diverse degrees. Seizures can also occur which is some cases can be early symptoms associated to mental deterioration. The association of central and peripheral neurological symptoms is very characteristic of MLD. The peripheral neuropathy is not generally clinically evidenced, but is rarely missing electrophysiologically. Arylsulfatase A determination should be performed for diagnosis as a first step, and confirmed by the accumulation of sulfatide, either by quantitative determinations in urine or by the sulfatide loading test. It is as yet not clear why certain forms have a rather rapid evolution in 5 years, and others have a very protracted course during decades.