In three letters written by Freud in 1908 and addressed to Jung, references were made to the addiction of their colleague, the rebellious and burlesque Otto Gross. It is most peculiar that these references are not mentioned in any of the surveys, reviews or texts dealing with Freud's ideas and theories on addiction. Freud's remarks on addiction in these letters, and indeed on the case of Otto Gross itself, are interesting enough to warrant (at least) a brief discussion. Gross was an assistant to the famous psychiatrist Kraepelin and a patient of Jung. Freud knew Otto's father, Hans, who was professor in criminology in Graz and Prague. Otto was a psychoanalyst and philosopher and he was also hopelessly addicted to cocaine and opium. Otto's addictive behaviour became at some point so problematic for his entourage that his father decided to have him locked away in a psychiatric institute. Needless to say that the relationship between father and son wasn't the best and it certainly didn't improve after the incarceration. Otto was, and remained, a troubled and rebellious character. He was freed after a while and then disappeared from the scene until his death, due to drug addiction, was announced in 1920.