People with schizophrenia are being let down by a patchy network of care and poor record-keeping, health watchdogs have warned.
Schizophrenia symptoms include delusions and hallucinations
A three-year inquiry into services for people with the mental illness across Scotland found "far too much variation" in the standard of care.
The NHS Quality Improvement Scotland (QIS) review found some progress since an earlier performance report in 2002.
There are 12,000 people in contact with services, according to the review team.
However, the report said: "No NHS organisation has a system to record all those with a diagnosis of schizophrenia and the actual number of people with the condition is likely to be higher than this figure."
Schizophrenia is a disabling mental illness where disordered thinking disturbs an individual's ability to function normally in society.
Symptoms can include delusions, hallucinations and catatonic movements.
There are an estimated 1,000 new cases of schizophrenia in Scotland expected every year, and the illness is one of the most costly conditions for the NHS to treat.
Many people with schizophrenia experience symptoms of varying degrees for many years and require help from a range of different agencies.
QIS chairman Lord Naren Patel said: "It's very disappointing that recommendations made in 2002 have still to be implemented in many parts of
"The same key messages are repeated in these latest findings.
"It is vital that action is taken now by those responsible for mental health
services to improve the care of people with schizophrenia."
Health minister Malcolm Chisholm pledged extra funds to support an existing
mental health information programme, but said boards were accountable for their
performance in delivering services.