| Country: | POL |
| Type: | DK |
| Route: | 91 |
| Established: | 2000 |
| Length Km: | 532.5 |
| Regions: | Pomeranian Voivodeship Kuyavian-Pomeranian Voivodeship Łódź Voivodeship Silesian Voivodeship |
| Cities: | Gdańsk, Tczew, Grudziądz, Toruń, Włocławek, Łódź, Piotrków Trybunalski, Częstochowa |
| Map: | Mapa DK91.png |
| Maint: | GDDKiA |
| Terminus A: | Gdańsk |
| Terminus B: | Podwarpie |
| Previous Type: | DK |
| Previous Route: | 90 |
| Next Type: | DK |
| Next Route: | 92 |
Droga krajowa nr 91 (translates from Polish as national road 91) is a route belonging to Polish national roads network. It runs from the seaport in Gdańsk to Częstochowa, and goes through the Pomeranian, Kuyavian-Pomeranian, Łódź and Silesian Voivodeships. Since this route was renumbered from DK1, it is frequently referred as "stara jedynka" (eng. "old one").
National road 91 is the alternative road for A1 motorway (partially tolled). As such, it runs parallel to:
Before 2000, road 91 ran from Gliwice–Rybnik–Wodzisław Śląski–Chałupki to the Czech border. This is now part of road 78.