The Portuguese patent law provides for such specific rules that apply to the first filing of patent applications by applicants having its corporate office in Portugal or with residence in Portugal. Article 76 of the Portuguese IP Code provides that where the applicant has its corporate office or residence in Portugal the European Patent application must be filed through the national office (unless a prior national Portuguese application is claimed). Where this requirement is not complied with, the patent will be of no legal effect in Portugal and the subsequent validation will be refused by the Portuguese Office.

According to the Decree-Law 42201 of 1959, the Portuguese Patent Office has to send all patent applications filed by applicants having its corporate office in Portugal or with residence in Portugal to the Department of the Defense Ministry. Within 5 days the invention should be analyzed to determine whether it is of interest to national defense and should remain secret. In practice, however, it appears that the secrecy regime was never applied.

In a recent decision of the Lisbon Court of Commerce the first filing rule was interpreted in stricter way. The case concerned an European Patent (EP) jointly owned by a Portuguese company, a US company and the Italian inventor. The EP validation was rejected by the Portuguese Office given that the EP was owned by a Portuguese company but it was not based on a prior national patent filed in Portugal (but in Ireland). The court reversed the Office decision considering that Article 76 should not apply to joint ownership of patents. The court found that the Office interpretation would unjustly harm the other non-Portuguese joint owners.