Grossdietwil is a municipality in the district of Willisau in the canton of Lucerne in Switzerland.

Of the agricultural land, 68.82% is used for farming or pastures, while 3.42% is used for orchards or vine crops.

Of the settled areas, 2.64% is covered with buildings, 0.1% is industrial, 0.39% is classed as special developments, 0.49% is parks or greenbelts and 2.15% is transportation infrastructure.

It consists of the village of Grossdietwil, the hamlets of Arpolingen and Kället and the exclave of Eppenwil.

Most of the population (as of 2000[update]) speaks German (93.4%), with Albanian being second most common ( 4.2%) and Portuguese being third ( 0.5%).

The age distribution, as of 2008[update], in Grossdietwil is; 251 people or 29.9% of the population is 0–19 years old.

In the 2000 census[update] the religious membership of Grossdietwil was; 660 (81.7%) were Roman Catholic, and 78 (9.7%) were Protestant, with an additional 5 (0.62%) that were of some other Christian faith.