The DSM-IV, the U.S. standard reference for psychiatry, includes over 300 different manifestations of mental illness. Psychiatrists themselves are in dispute over how common some of these conditions are, or whether they should be listed as 'mental illnesses', and each version of the DSM is slightly different to the previous ones.

The DSM-IV is currently being revised and updated, and the next version will include new-and-improved manifestations of illness. This is a portion of the currently recognised list of mental illnesses.

-- Acute stress disorder
-- Adjustment disorders
-- Agoraphobia
-- Alcohol and substance abuse
-- Alcohol and substance dependence
-- Amnesia
-- Anxiety disorders
-- Anorexia nervosa
-- Antisocial personality disorder
-- Asperger's disorder, also known as asperger's syndrome
-- Attention deficit disorder
-- Attention deficit/hyperactivity disorder
-- Autism
-- Avoidant personality disorder
-- Bereavement
-- Bibliomania
-- Binge eating disorder (proposed)
-- Bipolar disorder
-- Body dysmorphic disorder
-- Borderline personality disorder
-- Brief psychotic disorder
-- Bulimia nervosa
-- Cannabis addiction
-- Circadian rhythm sleep disorder
-- Conduct disorder
-- Conversion disorder
-- Cyclothymia (or Cyclothymic disorder)
-- Delusional disorder
-- Dependent personality disorder
-- Depersonalization disorder
-- Depression
-- Disorder of written expression
-- Dissociative fugue
-- Dissociative identity disorder
-- Dyspareunia
-- Dysthymic disorder
-- Encopresis
-- Enuresis (bedwetting)
-- Exhibitionism
-- Expressive language disorder
-- Female and male orgasmic disorders
-- Female sexual arousal disorder
-- Fetishism
-- Folie - deux
-- Frotteurism
-- Gender identity disorder
-- Generalized anxiety disorder
-- General adaptation syndrome
-- Histrionic personality disorder
-- Hyperactivity disorder
-- Primary hypersomnia
-- Hypoactive sexual desire disorder
-- Hypochondriasis
-- Hyperkinetic syndrome
-- Hysteria
-- Intermittent explosive disorder
-- Joubert syndrome
-- Kleptomania
-- Down syndrome
-- Mania
-- Male erectile disorder
-- Munchausen syndrome
-- Mathematics disorder
-- Mental retardation (strictly this is not a mental illness)
-- Multiple personality disorder
-- Narcissistic personality disorder
-- Narcolepsy
-- Nightmare disorder
-- Obsessive-compulsive disorder
-- Obsessive-compulsive personality disorder
-- Oppositional defiant disorder
-- Pain disorder
-- Panic attacks
-- Panic disorder
-- Paranoid personality disorder
-- Pathological gambling
-- Pedophilia
-- Pica
-- Post-traumatic stress disorder
-- Premature ejaculation
-- Primary insomnia
-- Psychotic disorder, not otherwise specified
-- Pyromania
-- Reading disorder
-- Retts disorder
-- Rumination disorder
-- Schizoaffective disorder
-- Schizoid personality disorder
-- Schizophrenia
-- Schizophreniform disorder
-- Schizotypal personality disorder
-- Seasonal affective disorder
-- Separation anxiety disorder
-- Sexual Masochism and Sadism
-- Shared psychotic disorder
-- Sleep disorder
-- Sleep terror disorder
-- Sleepwalking disorder
-- Social phobia
-- Somatization disorder
-- Specific phobias
-- Stereotypic movement disorder
-- Stuttering
-- Tourette syndrome
-- Transient tic disorder
-- Transvestic Fetishism
-- Trichotillomania
-- Vaginismus
-- Voyeurism

http://www.fact-index.com/m/me/mental_illness__alphabetical_list_.html