An applicant desiring to take advantage of the priority of a previous application must file a declaration of priority and any other document required, in accordance with the Implementing Regulations (Art. 88 EPC). Under R. 52(2) EPC, a declaration of priority shall preferably be made on filing the European patent application, but it may still be made with sixteen months of the earliest priority date claimed. This is a significant relaxation of the requirements as compared to R. 38(2) EPC 1973, under which at least the date and the state of the previous application had to be indicated on filing.

Similarly, R. 53 EPC (R. 38(3) EPC 1973) provides that an applicant claiming priority shall file a copy of the previous application within sixteen months of the earliest priority date claimed.

In J 1/80 (OJ 1980, 289) it was stated that as R. 38(3) EPC 1973 permitted an applicant to file certified copies of the priority documents at any time before the end of the sixteenth month after the date of priority, there was only a deficiency which he must be given an invitation to correct if the priority documents had not been filed at the end of the period.