This page compares two distinct NUCC-taxonomy specialties tracked by the CMS National Plan and Provider Enumeration System: Clinical Psychologist, which currently counts 63,000 enrolled providers across 56 U.S. states and territories, and Health Service Psychologist, with 906 providers across 49 states. Each clinician on these rosters selected a primary NUCC code at NPI enrollment, so the totals measure how many providers self-identify their primary practice as Clinical Psychologist or Health Service Psychologist rather than the total population ever trained or credentialed in either field — dual-certified clinicians show up under whichever code they registered first.

On national volume, Clinical Psychologist carries the larger provider roster (63,000 vs 906), and Clinical Psychologist has the wider geographic footprint at 56 states versus 49. The top Clinical Psychologist concentration sits in California (11,040 providers), while Health Service Psychologist peaks in California (89). The per-capita columns in the table below normalize each state's raw count against 2023 Census population estimates, which matters because absolute provider counts track population scale first and specialty density second — a small state with a strong training pipeline can out-rank a larger state on per-100K availability.

Use this comparison to understand relative availability, not to judge clinical substitutability — Clinical Psychologist and Health Service Psychologist are distinct specialties with different scopes of practice, training requirements, and conditions they treat, even when their NUCC categories overlap. Important: PlainDoctor is a directory of publicly available CMS government data, not medical advice, a provider rating, or a recommendation about which specialty a patient should consult. Always work with a licensed clinician to determine which specialty is appropriate for your condition, verify any specific provider through the NPPES NPI Registry and the relevant state medical board, and consult the NUCC taxonomy documentation for the formal scope-of-practice definitions behind each specialty code.