The guitar great tells Britain's Birmingham Mail he's beginning to feel the affects of old age after fighting lymphoma for much of the band's reunion.
He says, "I can't actually do this anymore. My body won't take it much more."
Iommi has won the first round of his battle with the disease, but it has left the musician weak - and he's certain the cancer will return.
The guitarist adds, "I don't want that creeping back again, and all the traveling involved in Sabbath tours increasingly takes its toll. That's why we're going out on one last tour, to say our farewells. And then it very definitely is the end. We won't be doing it again."
The final Black Sabbath tour will begin in Nebraska in January (16). Dates in North America and Australasia were announced last week (ends04Sep15), but Iommi assures fans in Europe and Asia they can also look forward to final concerts, adding, "There will be U.K. dates and of course we'll be playing Birmingham. This is where it all began for us; this is where family and friends live; this is where our longest-standing fans are. It would be unimaginable for the Sabbath farewell tour not to include Birmingham. But you'll have to bear with us. The logistics are still being worked out. Even we don't know all the dates yet."