The symptoms which came to be known as “Haff disease” were observed for the first time in the summer of 1924. The phenomenon was associated with the formerly East Prussian coastal region around the “Frisches Haff” (the Vistula Lagoon, an inlet of the Baltic Sea). A fisherman had experienced signs of paralysis accompanied by severe muscular pain. The disappearance of the disease was just as mysterious as its occurrence. The example of Haff disease is of mainly historical significance today. Haff disease is a fine example of a disease of civilization whose causes may remain unexplained as they were only of temporary importance. It is likely that the symptoms were triggered by a toxin (heavy metal or arsenic) and were connected to direct contact with fish.