| Name | Track | Diplomate Status | Certified Date | Expires |
|---|---|---|---|---|
| Sunila E. O'Connor | EM | Diplomate | 5/21/2001 | 12/31/2031 |
| Cormac O'Donovan | EP | Diplomate | 10/30/1999 | Never |
| Blake B. O'Lavin | EEG | Diplomate | 12/5/1976 | Never |
| Rachel Frances Ochs | CNP | Diplomate | 9/16/1984 | Never |
| A. O. Ogunyemi | CNP | Diplomate | 9/20/1987 | Never |
| Minoru Oishi | CNP | Diplomate | 12/31/1983 | Never |
| Yumiko Okahashi | EM | International | 6/18/2022 | 12/31/2032 |
| Barry S. Oken | CNP | Diplomate | 9/16/1984 | Never |
| Piotr Olejniczak | EM | Diplomate | 4/17/1999 | 12/31/2019 |
| Nick Olmos-Lau | EEG | Diplomate | 4/30/1978 | Never |
| Richard K. Olney | CNP | Diplomate | 9/16/1984 | Never |
| Donald M. Olson | CNP | Diplomate | 10/1/1988 | Never |
| Walter Olson | CNP | Diplomate | 6/14/1981 | Never |
| Sandra F. Olson | EEG | Diplomate | 12/31/1969 | Never |
| Betty Y. Ong | CNP | Diplomate | 10/1/1988 | Never |
| Ligia V. Onofrei | NIOM | IOM Diplomate | 11/30/2020 | 12/31/2030 |
| K.J. Oommen | CNP | Diplomate | 12/31/1986 | Never |
| Daniel San Juan Orta | CNP | International | 6/13/2026 | 12/31/2036 |
| Daniel San Juan Orta | IOM | International | 11/16/2024 | 12/31/2034 |
| Afag M. Osman | CNP | International | 6/20/2015 | 12/31/2035 |
| Ivan Osorio | CNP | Diplomate | 4/27/1985 | Never |
| Joel M. Oster | NIOM | Diplomate | 6/20/2015 | 12/31/2035 |
| Joel M. Oster | CC-EEG | Diplomate | 10/24/2015 | 12/31/2035 |
| Joel M. Oster | EM | Diplomate | 10/28/2007 | 12/31/2027 |
| Mortimer Ostow | EEG | Diplomate | 12/31/1952 | Never |
|
1674 Certificants
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