What the RDMS is, the specialties it covers, how it is earned, and what it takes to keep it active.
The RDMS — Registered Diagnostic Medical Sonographer — is the most common credential in general sonography. It is issued by the American Registry for Diagnostic Medical Sonography (ARDMS), and for most prospective students it is the credential they are working toward. It is earned only by examination, and it is held in a specific specialty.
What the RDMS covers
The RDMS is awarded in a chosen specialty rather than as a single general title. The specialties available under it include Abdomen, Obstetrics and Gynecology, Breast, Fetal Echocardiography, and Pediatric Sonography (ARDMS). A sonographer becomes registered in one of these, and many add more over a career. The related ARDMS credentials cover other areas: the RDCS covers the heart and the RVT covers blood vessels.
How it is earned
There is only one path to the RDMS, and it runs through exams: ARDMS credentials are earned by examination, and an applicant must meet the prerequisites before sitting (ARDMS). The structure is two exams:
- The SPI exam — Sonography Principles and Instrumentation, the physics exam that every ARDMS credential requires. The SPI Physics Exam page covers it in full.
- A specialty exam — for example, the Abdomen exam or the OB/GYN exam.
The two can be taken in either order, but once the first is passed, the second must be passed within five years (ARDMS). Passing both, with the prerequisites met, earns the RDMS in that specialty. The most common way to meet the prerequisites is graduating from an accredited program; Accreditation explains why that matters.
Keeping it active
The RDMS is not a one-time achievement. It is maintained through the ARDMS Maintenance of Certification (MOC) program, which all active registrants must follow (ARDMS). MOC runs on a recurring three-year continuing-education cycle, alongside an annual attestation and an annual renewal fee. Letting these lapse can place the credential in an inactive status.
Why it matters
Certification through a body whose exams are accredited by recognized agencies is considered the standard of practice in sonography (Society of Diagnostic Medical Sonography). In practice, that means most employers expect a sonographer to hold the RDMS or an equivalent credential, which is why the credential — not the degree alone — is the real entry point to the field. Licensing and Certification covers how certification differs from a state license.
Last verified: 2026-06-14. Credential requirements and fees change; confirm current details with ARDMS. This page is informational and does not recommend a credential or program.