It's hard to determine where the serial number is located. I thought it was the orange shipping label on the side of the mattress. I pulled that off when the mattress was placed on the frame. Since then, the padding and sheets were placed on the bed. I went to fill out the warranty and none of those numbers worked. On the little instruction sheet, it says the s/n is located under the bar code. Confusing as the orange shipping tag has bar codes with a few numbers under the bar code. It wasn't until I stripped the bed and raised that mattress that I found a decal that stated "Warranty void if removed" with a bar code an number below the bar code. I finally got a picture of that and was able to enter. Other than that, the mattress is great, and I am enjoying the adjustable base I purchased with the mattress.