My husband recently had surgery and they found three positive lymph nodes, but no other signs that the cancer had spread. Does it make sense to have chemo and radiation?

With positive lymph nodes, the chance of the cancer coming back is high enough, that it is considered standard to consider chemotherapy, as it improves survival. His general medical condition and any other problems that he may have will also need to be considered.

It makes sense for your husband to strongly consider treatment as the benefits usually outweigh the risks. He may not need radiation if he has colon cancer.