The 1991 German Open was a men's tennis tournament played on outdoor clay courts.

It was the 85th edition of the Hamburg Masters (Hamburg Masters), and was part of the Championship Series category of the 1991 ATP Tour.

It took place at the Rothenbaum Tennis Center in Hamburg, Germany, from 6 May until 13 May 1991.

Karel Nováček, who was seeded 13th, won the singles title.

[3] Karel Nováček defeated Magnus Gustafsson, 6–3, 6–3, 5–7, 0–6, 6–1 Sergio Casal / Emilio Sánchez defeated Cássio Motta / Danie Visser, 4–6, 6–3, 6–2