Značajniji kongresi održani u Opatiji od 1885. do 1976. godine 1885.
Congress of Doctors Balneologists
1904.
Congress of Austrian Balneologists
1908.
IV International Congress for Thalassotherapy
1933.
Convegno Nazionale Alberghi e Turismo
1951.
4th International Conference ICTM (International Council for Traditional Music)
1953.
General Meeting of the International Electrotechnical Commission (IEC)
1954.
Congress International Handball Federation
1954.
International Congress of Hydroclimatisme and Thalassotherapy
1959.
12th Annual Assembly of the International Institute of Welding
1959.
8th Round Table of the International Political Science Association
1960.
Red Cross International Seminar
1961.
Conference International du Droit Maritime
1961.
World Congress of World Association of Travel Agents (WATA)
1961.
3rd World Congress of the International Association for Mathematics & Computers in Simulation (IMACS)
1961.
6th International Conference on Lightning Protection (ICLP)
1962.
13th Congress AIEST (Association International des Experts Scientifiques de Tourisme)
1963.
International Congress of Military Medicine
1963.
Moto Rally F.I.M
1964.
International Congress of Agriculture
1965.
Congress FIJET (Federation International des Journalistes de Tourisme)
1966. 3rd General Assembly BITS (International Bureau of Social Tourism)
1933. godine u Opatiji je održan Nacionalni kongres hotela i turizma Italije
1985. godine održan je Europski kongres za prevenciju alkoholizma i ovisnosti o drogi
VI. Svjetski kongres socijalne psihijatrije održan je od 4. do 10. listopada 1976.
4. Međunarodni kongres kardijalne kirurgije održan je u hotelu Kvarner 1997. godine
1966.
25th Annual Meeting ALPS
1967.
World Congress International Federation of Freight Forwarders Associations (FIATA)
1968.
5th Congress World Association for Buiatrics
1968.
21st Congress of the European Society for Opinion and Marketing Research (ESOMAR)
1969.
Symposium of INSEA (The International Society for Education through Art)
1970.
8th World Congress of International Academy for Court and Social Medicine
1970.
7th General Assembly of Meditercongress
1971.
International Conference for the Sociology of Religions (SISR)
1971.
28th FIS Ski Congress
1975.
8th European Regional Symposium on Social Welfare (ICSW)
1975.
16th Congress for Thalassotherapy
1976.
6th World Congress of the World Association for Social Psychiatry (WASP)
1976.
Annual Meeting National Drink and Food Association (UK)
1976.
2nd Conference of Mediterranean Cities – Protection against Pollution
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