At the beginning of his career, he took 7th at Debrecen 1913 and tied for 4-5th at Kaschau 1918, both in B tournaments.
After World War I, Mendelssohn played in many tournaments in Bucharest.
[1] He also took 4th at Jassy (Iaşi) 1929 (ROM-ch, Tyroler won), and took 6th at Cernăuţi 1930 (ROM-ch, János Balogh won).
Mendelssohn played for Romania in 2nd unofficial Chess Olympiad at Budapest 1926, and won team bronze medal there.
[2] This biographical article relating to a Romanian chess figure is a stub.