I actually work in the field of medical records and coding! For diagnosis coding we use (in the us) ICD-9-CM. the cm is for the united states. Other countries are using ICD-10. The DSM is also used for mental illness.

Many mental health professionals use the manual to determine and help communicate a patient's diagnosis after an evaluation; hospitals, clinics, and insurance companies in the US also generally require a DSM diagnosis for all patients treated. The DSM can be used clinically in this way, and also to categorize patients using diagnostic criteria for research purposes.