CPT Code 90791 is the first code used when a provider begins sessions with new patients. It marks the beginning of all future coding and billing efforts that a provider will have with a patient. Here we explore it’s importance, usage, details, and more.

CPT Code 90791 is used for a psychiatric diagnostic evaluation without medical services. This is typically the initial assessment performed by a mental health provider when a new patient begins treatment. If an established patient medically requires reassessment, in case of long absences or significant changes in their established condition, CPT code 90791 can be used again.

Unlike therapy session codes, CPT code 90791 focuses on evaluating the patient’s mental health status, history, and treatment needs. It is an essential part of building a clinical picture and determining the next steps in care.

What Is CPT Code 90791?

90791 represents a comprehensive diagnostic interview that may include interviews with family members, a review of medical and psychiatric history, and the use of mental status examination tools. It is performed by psychologists, therapists, and clinical social workers. If a psychiatrist or other medical professional performs the evaluation with medical services, they would typically use CPT code 90792 instead.

The service does not require a specific duration, but sessions often last 60 minutes or more to cover the required components. If a diagnostic interview can comprehensively be completed in less than 60 minutes, it is still correct to code for CPT code 90791 for the session.

When to Use CPT 90791

Use this code when conducting a formal intake assessment for a new patient. The session should include gathering background, reviewing prior diagnoses, and forming a preliminary treatment plan.

It may also be used when a patient is re-evaluated after a long absence or significant change in condition.

Documentation and Reimbursement

Documentation should cover:

Reason for evaluation
Clinical observations
Mental status findings
Diagnosis and recommendations

Reimbursement typically falls between $120 and $160, depending on the payer and location where the service is provided. This is a one-time-per-provider service unless medically necessary for reassessment.

By choosing to partner with a specialized medical billing company—especially one focused on mental health billing services—you can streamline your practice’s financial operations and optimize CPT code 90791 claims processing. Expert billing teams understand payer-specific rules, documentation requirements, frequency limits, and allowable reimbursement rates for psychiatric diagnostic evaluations. They help ensure claims are clean, complete, and compliant, reducing denials and accelerating payment cycles.

Working with a mental health billing service also means having dedicated support for appeals, modifier use (such as telehealth modifiers 95/GT or interactive complexity CPT 90785), and eligibility verification. When you leverage certified mental health billing experts, you not only increase revenue accuracy, but also free your clinical staff to focus on patient care—while the administrative details are handled reliably and proactively.

Who can bill 90791?

Non-medical mental health professionals such as psychologists, therapists, and LCSWs.

How long should the session be?

While there's no exact time rule, most sessions last 60 minutes or more.

CPT Code 90791: Psychiatric Diagnostic Evaluation Explained