We evaluated the effect of combining lenalidomide with therapeutic antibodies on antibody-dependant cell-mediated cytotoxicity (ADCC) of solid tumor cells, and the requirement for expression of natural killer (NK) cell-activating receptors and their solid tumor surface ligands. Twenty-three human tumor cell lines (colon, breast, lung, head and neck, ovary, and bone sarcoma) were analyzed. NK effector cells were isolated from healthy donors, pre-treated with and without lenalidomide, and incubated with antibody-coated tumor cells to determine ADCC. In blocking experiments, NK cells were pre-incubated with anti-DNAM-1 or anti-NKG2D antibodies, and target colorectal cells were pre-incubated with anti-CD155 (PVR), anti-MIC-A/B, or anti-ULBP 3 antibodies. Differences between groups were assessed using unpaired and paired Student's t test and one-way ANOVA. Lenalidomide enhanced NK cell-mediated ADCC of trastuzumab- and cetuximab-coated tumor cells. Activity against colorectal cancer cells was dependent on target antigen expression, but independent of KRAS status and FcγRIIIa genotype. The extent of ADCC and its enhancement by lenalidomide correlated with NK cell expression of NKG2D and DNAM-1, and tumor cell expression of PVR and MIC-A. Blocking of NKG2D and, to a lesser extent, DNAM-1 inhibited ADCC. Anti-MIC-A/B monoclonal antibody blocked natural cytotoxicity, but not ADCC. Lenalidomide enhances the ability of IgG1-isotype antibodies to mediate ADCC of solid tumor cells, the extent of which is largely dependent on NKG2D-NKG2D ligand interactions, but appears to be independent of MIC-A/B. This provides a rationale for exploratory clinical studies and an assessment of potential biomarkers predictive of clinical benefit.