My father died about 5 years ago from multiple myeloma. I was the bone marrow donor for his transplant. I am an only child and am wondering about my risk factor for myeloma, especially since my marrow was considered a good match.

NCI Study... An nci study is looking at characterizing families that may be at higher risk to identify causes: screening individuals and families at high risk for hematologic cancers nct00052234 http://clinicaltrials.Gov/ct2/show/nct00052234?Term=nct00052234&rank=1.
About 2X risk. Sorry to hear about your dad.Being a donor doesn't change your risk. Multiple myeloma is not classically thought of as a familial/inherited cancer. However, the risk of a hematologic malignancy (mm, lymphoma, leukemia) in family members is thought to be about two times higher.