Psychiatry’s number one diagnostic manual is being re-written — and it’s making everyone crazy. Gender identification disorder may be in, while sleepwalking disorder is on the outs. By 2012, the American Psychiatric Association hopes to have published a new edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM) — the diagnostic manual used to determine if a patient has a mental disorder. Proposed changes are already being challenged by patients, insurance companies, and the pharmaceutical industry. The New York Times science journalist Benedict Carey explains.