We have studied the polymerization of methyl methacrylate with cesium and tetramethylammonium salts of diethyl 2-ethylmalonate carbanion. For polymerizations initiated at room temperature, no effort was made to control the exotherm. The polymerizations proceeded with high conversions and produced polymers characterized by broad polydispersities (M-w/M-n = 2-3). We consistently observed M-n (exptl) < M-n- (calcd) for target = 50,000-300,000 g/mol; we observed an apparent upper limit for M-n, of 60,000-70,000 g/mol. Chain transfer from impurities in reagents was eliminated as the source of molecular weight lowering. Oligomeric samples were analyzed by mass spectrometry; results were best explained by methoxide initiation of the polymerization. No evidence for malonate end groups was observed in the mass spectra.