The general accessibility and high accuracy of GPS caused that for a dozen or so years it is applied commonly, not only in marine navigation. We can ascertain that in this regard there exists the monopoly. However, now it is apparently that this system can be easily disturbed, what testify numerous reports. The problem has been treated as troubles in land navigation, however nowadays became every-day reality on coastal waters as well, especially on the Mediterranean and Black Seas and Persian Gulf. Officers who survived this tell that the first impulse in such situation is to verify GPS receiver, regardless of the situation around the ship. The concentration of the officer’s attention on the GPS receiver, especially on coastal waters creates the threat for the ship, however in this situation appear other threats which many officers does not associate with GPS. Usually on the present ship GPS receiver is not only the source of positioning information. It is a source of information for many other devices, so inappropriate work of it generates problems with many other processes on the ship. Today question is who on the bridge can notice GPS problems and how? There are receivers which do not inform about the problem, or present not realistic data. Sometimes only ECDIS picture shows some abnormality, for example still the same position while ship is under the way. On the paper the analysis of possibly aspects of the problem is discussed. Presented analysis goes to the conclusion that should be prepared some procedure how to proceed in case of the lack of GPS signals, as well as the watch officer should be prepared to act in such situation. This is a task for marine academies.