How many psychiatrist appointments will it take to get yourself a diagnosis?

One. When you see a psychiatrist, he or she should be able to give you a diagnosis at the first appointment. In rare cases, it may take a follow up to gather additional information from other sources.
It depends. When you see a psychiatrist, he or she should be able to give adult a diagnosis at the first appointment. In rare cases, it may take a follow up to gather additional information from other sources. In the case of children and adolescents it is not uncommon to use 1-2 sessions to arrive at an appointment and recommended treatment plan.
Accurate information. Several factors are involved in making a psychiatric diagnosis. If all the factors are readily available and accurate most diagnoses can be made in a single visit. But that is not always the case. The important factors are: a reliable description of the presenting problem by the patient, an accurate history, and accurate collateral information. If any of these are missing it may take more visit.