Scrape gills from mushroom caps with a spoon, if desired.
Combine vinegar, oil, and salt in a shallow dish or large zip-top plastic freezer bag; add mushrooms, turning to coat. Cover or seal, and chill 1 hour, turning occasionally. Remove mushrooms from marinade, discarding marinade.
Grill mushrooms, covered with grill lid, over medium-high heat (350° to 400°) 3 to 4 minutes on each side or until tender.