Lignin concentration is strongly negatively correlated with in vitro digestibility of neutral detergent fiber (IVNDFD) when examined across a wide forage maturity range, but this relationship is less clear among forages of similar maturity. We examined the relationships of IVNDFD with lignin and other cell wall traits for alfalfa stems for two maturity stages and multiple annual harvests. Eight germplasm sources (ranging from commercial high-quality and lodging resistant varieties to experimental biomass and rooting germplasms) were planted at Becker, MN and Arlington, WI in 2004 in replicated plots in a randomized complete block design. Stem material was harvested four times annually at the early bud stage and three times at late flower in 2005 and 2006. Neutral detergent fiber (NDF), acid detergent lignin (ADL), Klason lignin (KL), total cell wall (CW) concentration and polysaccharides (cellulose, hemicellulose, and pectin), and 16- and 96-h IVNDFD were determined by near-infrared reflectance spectroscopy. Pearson correlations were computed across the entire experiment, by maturity, by harvest, and for maturity x harvest combinations.  Surprisingly, 16- and 96-h IVNDFD were inconsistently correlated (positive, negative, and non-significant) for maturity and harvest. While KL, NDF, and CW concentrations were negatively correlated with 16-h IVNDFD over the entire data set, ADL concentration was non-significant. No traits were correlated with 16-h IVNDFD for all data subsets; although KL as a proportion of NDF was negatively correlated with 16-h IVNDFD for all maturity x harvest combinations except the first early bud harvest. Greater consistency was observed for 96-h IVNDFD where correlations of NDF (negative), ADL (negative; proportion of dry matter or NDF), and proportion pectin in the cell wall (positive) concentration were found with all maturity x harvest combinations. Concentration of KL was not consistently correlated with 96-h IVNDFD. These data illustrate the difficulty in predicting fiber digestibility from composition.