Attempted preparation of omega-formyl-functionalized polydienes by termination of poly(butadienyl)lithium and poly(isoprenyl)lithium with 8-morpholinecarboaldehyde resulted in 73 and 38% dimer formation (SEC), respectively, under conditions that quantitativey produced omega-formyl-functionalized polystyrene. Dimer formation was attributed to postfunctionalization, base-catalyzed, aldol-type condensation based on FTIR and H-1-NMR analysis of the dimer products. High yields (>97%) of omega-formyl-functionalized polydienes were formed by workup using acidic methanal; quantitative functionalization resulted from end capping the polymeric organolithium chain ends with 1,1-diphenylethylene prior to the functionalization reaction. The omega-formylpolydienes were characterized by hydroxylamine end-group titration, FTIR, and both H-1- and C-13-NMR spectroscopy.