The role of 1,25-dihydroxyvitamin D 3 (1,25-(OH)2 D 3 ) as a regulator of cell growth and differentiation is well recognized. Currently, 1,25-(OH)2 D 3 and vitamin D analogs are being evaluated for their therapeutic potential in the treatment of hyperproliferative disorders like cancer. In the present review, we will discuss several processes that might be involved in 1,25-(OH)2 D 3 - and vitamin D analog-mediated suppression of cancer cell growth. The effects on tumor cell proliferation, differentiation, apoptosis, angiogenesis, metastases, and parathyroid hormone-related peptide secretion will be highlighted. In addition, combination therapy with other tumor effective drugs will be addressed. Furtermore, we will focus on the potential drawbacks and the possible side effects of vitamin D compounds in the treatment of cancer.