Physicians in radiation oncology and other interested individuals in other radiation oncology-related occupations outside of the United States are able to join ASTRO and receive all of the regular benefits and services available to U.S. members.
ASTRO has more than 1,700 international members from every continent, covering more than 75 countries from around the world. The primary member categories are International, Correspondng and International Member-in-Training.
ASTRO International Membership Representation:
(there are 32 countries with more than 10 members each)
| Country | Number of Members | Country | Number of Members |
| Argentina | 25 |
Japan | 233 |
| Australia | 81 |
Mexico | 34 |
| Austria | 29 |
(The) Netherlands | 122 |
| Belgium | 40 |
New Zealand | 19 |
| Canada | 411 |
Phillipines | 14 |
| Chile | 20 |
Poland | 11 |
| China | 23 |
Saudia Arabia | 15 |
| Egypt | 18 |
Singapore | 16 |
| France | 65 |
South Africa | 16 |
| Germany | 176 |
South Korea | 52 |
| Greece | 20 |
Spain | 39 |
| Hong Kong | 17 |
Sweden | 20 |
| India | 53 |
Switzerland | 31 |
| Ireland | 21 |
Taiwan | 40 |
| Israel | 17 |
Turkey | 42 |
| Italy | 70 |
England/UK | 99 |
Countries with 10 or fewer ASTRO members each include:
| Albania | Morocco |
| Bangladesh | Myanmar |
| Bulgaria | Netherlands Antilles |
| Bulgaria | Nigeria |
| Columbia | Norway |
| Costa Rica | People's Republic of China |
| Croatia | Pakistan |
| Cyprus | Panama |
| Czech Republic | Paraguay |
| Denmark | Peru |
| Ecuador | Portugal |
| Finland | Qatar |
| Ghana | Romania |
| Guatemala | Russia |
| Holland | Slovak Republic |
| Hungary | Syria |
| Indonesia | Thailand |
| Iran | Tunisia |
| Jamaica | United Arab Emirates |
| Jordan | Uruguay |
| Kuwait | Venezuela |
| Lebanon | Yemen |
| Macedonia | Yugoslavia |
| Malaysia |