| Date: | 15–21 May |
| Edition: | 70th |
| Category: | Grand Prix (Four star) (men) Colgate Series (A) (women) |
| Surface: | Clay / outdoor |
| Draw: | 64S/32D |
| Prize Money: | $175,000 (men) $35,000 (women) |
| Location: | Hamburg, West Germany |
| Champms: |  Guillermo Vilas[1] |
| Champws: | Mima Jaušovec |
| Champmd: | Tom Okker /  Wojciech Fibak[2] |
| Champwd: | Mima Jaušovec /  Virginia Ruzici |
| Before Name: | German Open |
The 1978 German Open was a combined men's and women's tennis tournament played on outdoor red clay courts. The men's tournament was part of the 1978 Colgate-Palmolive Grand Prix circuit, categorized as a four-star event, while the women's tournament was part of the Colgate Series and classified as an A category event. It was the 70th edition of the tournament and took place at the Am Rothenbaum in Hamburg, West Germany, from 15 May through 21 May 1978. Guillermo Vilas and Mima Jaušovec, both first-seeded, won the singles titles.[3] [4]
Guillermo Vilas defeated Wojciech Fibak 6–2, 6–4, 6–2
Mima Jaušovec defeated Virginia Ruzici 6–2, 6–3
Tom Okker / Wojciech Fibak defeated 
Antonio Muñoz / Víctor Pecci 6–2, 6–4
Mima Jaušovec / Virginia Ruzici defeated Katja Ebbinghaus / Helga Masthoff 6–4, 5–7, 6–0