Yes Mad!
You can substitute sweet potatoes, carrots, squash and also turnips.
They will all taste like pumpkin when you add the spices.
Dolly

I had sweet potato pie once and couldn't tell the difference from pumpkin.

yes. I often do.
I've made the cookies below with pumpkin puree and sweet potato puree..tasted the same pretty much..
They are really good!

Here is a link that might be useful: Iced Pumpkin Cookies

I always heard you can substitute squash, sweet potatoes, yams and pumpkin.

When my family thinks we are having Pumpkin Pie we are actually having this. It's so good and not as coarse as pumpkin.

Sweet Potato Pie

3 eggs
1 C. Sugar
1 C. cooked sweet potatoes, mashed (I buy the canned ones)
3/4 C. evaporated milk
1/3 C. regular milk
1/4 C. melted butter
2 tsp. vanilla
1/2 tsp. pumpkin pie spice
10" unbaked pie shell

Preheat oven 400.

Beat together the eggs, sugar and potatoes. Add milk, butter, spice and vanilla. Pour in pie shell and bake 10 minutes. Lower oven temp. to 325 and bake for 35 minutes or until knife comes out clean.

We had company for dinner last night and I made pumpkin pie for dessert. The recipe was from Cook's Illustrated. It used 1 can pumpkin, 1 can drained canned yam in syrup, heavy cream, milk, eggs, etc. I am not a big pumpkin pie fan, but I have to say this was the best pumpkin pie I ever had. No one noticed there was yam (sweet potato) in it.

I have been using Kabocha squash as a substitute and find the flavor even better.
I am using butternut squash this week for smoothies and it is good but not as good as Kobocha squash. It is also called Japanese pumpkin.

Thanks for your replies! I was gifted with a box of sweet potatoes after I had bought a box and was wondering if I could interchange them.

So let me get this straight...I want to make a pumpkin bundt cake.....I should drain the canned sweet potatoes, mash them and use the same measurement that the recipe calls for mashed pumpkin, right?

Linda, I've done that with success. But I'd probably ask also in the cooking forum. But I did use canned sweet potatoes but take note some are in a sweetened juice which is what I used..after I drained them I gently folded them in a paper towel to absorb some of the moisture clinging to them. End result for me was delish and no one knew it was made with sweet potatoes from a can...actually I think the cake was more moist.

good idea to remove as much of the juice by wrapping in a paper towel....moisture can make a soggy cake....thanks for the tip