The current psychiatric manual, the fourth edition Diagnostic and Statistical Manual categorizes Aspberger syndrome and autism as different disorders. Asperger's Syndrome is on the autism spectrum however it is still questionable whether it is different from High Functioning Autism, and so it has already been proposed that the category be eliminated in favor of diagnosing the severity of autism in a person.
While autism was first described by Leo Kanner in 1943, the name Asperger comes from Austrian pediatrician Hans Asperger who made a case study of children who lacked nonverbal communication skills, empathy for their peers and were physically clumsy. The study was made in 1944 but was only popularized in 1981 and from then onwards became a different, if similar diagnosis from autism. The real inherent difference between Asperger's and autism is the fact that children and adults with Asperger do not suffer from any speech impediment. They do, however, posses an obsession with one subject in particular and have a problem empathizing with the world outside of themselves. Asperger himself disagreed that what he described was variant of Kanner's autism.
The problem with categorizing Aspergers as a more mild for of autism is the fact that it implies Asperger patients have lesser difficulties in life than those with autism. In reality, Asperger patients can have much greater anxieties and greater depressions than autistic patients not to mention their larger awareness of the world makes understanding the real stigma behind their condition much easier.
The current diagnosis of Aspergers is on the rise, however the category only began to exist around 20 years ago after Asperger's study was translated to English in 1981. Therefore psychologists are probably more adept at detecting it than they were when just starting out. Hopefully through clearer understanding of the disorder as research goes on psychologists will reach a consensus that will help patients function as well as possible in our society.