| Image Coa: | DEU Grethem COA.svg |
| Coordinates: | 52.7167°N 44°W |
| Image Plan: | Grethem_in_HK.svg |
| State: | Niedersachsen |
| District: | Heidekreis |
| Samtgemeinde: | Ahlden |
| Elevation: | 24 |
| Area: | 16.35 |
| Postal Code: | 29690 |
| Area Code: | 05164 |
| Licence: | FAL, SFA |
| Gemeindeschlüssel: | 03 3 58 011 |
| Website: | www.grethem.de |
| Mayor: | Udo Schönberg |
Grethem is a municipality in the district of Heidekreis, in Lower Saxony, Germany.