The authors of the text have been particularly interested into the organization, the procedure,the accompanying activities as well as the themes covered at 4th International Congress of Thalassotherapy in Opatija in 1908. The Congress was organised by the then head of the thermal spa resort Professor Dr.Julius Glax. The official languages at the Congress were German, French, English, and also Italian and Croatian as the languages of the hosting country. Each lecturer had twenty minutes time to give a lecture or a co-lecture, ten minutes for papers and five for a follow-up discussion. The participants could make use of the information centre of the Congress, in the centre of Opatija, the whole day. Unofficially, the Congress started on 27th September 1908 with the introductory evening for all the participants in Adria Club. The Congress officially began on 28th September 1908 when all the participants gathered at the theatre hall of Hotel Stephanie. The lectures were presented in the morning. In the afternoon, the participants were taken to visit some exhibitions (e.g. the medical exhibition at Hotel Palace, the exhibition of the native Istrian-Dalmatian home crafts and antiquates and the painting exhibition at Vila Angiolina), a short sea voyage through the bay of Kvarner. On the last day of the Congress, the participants observed the sanitary conditions in Opatija (the water supply, the sewer system, litter incinerator, and quarantine for infectious illnesses), three sanatoriums, Zander's Institute, the rehabilitating-heart paths and the Archduke Ludwig-Viktor's indoor baths. The round-Opatija tour was followed by the concluding meeting and the conclusion of the Congress. The authors of this research have established that there are no important differences in the organization and realization of the congresses in the past and now.