Clinicians and researchers use body composition measurements to identify individuals who may be at risk of adverse health complications. This study compared two commonly used two-compartmental anthropometric models (bioelectrical impedance analysis [BIA] and air displacement plethysmography [ADP]) to determine whether these two cost-effective methods would provide similar fat free mass index (FFMI) values in a mixed and sex-separated sample population of healthy older adults. Community-dwelling older adults (N = 37, 18 men) aged 74.5 ± 5.2 years participated. FFMI_BIA was correlated with FFMI_ADP (r = .916); however, these correlations were markedly reduced when the population was split by sex (r < .60). The level of agreement between the difference values (FFMI_BIA – FFMI_ADP) fluctuated ± 2.1 kg/m² (illustrated via Bland-Altman plots), but these differences were not statistically different from 0. Findings from the current work suggest that clinicians must be cautious when using portable devices such as BIA to assess FFMI in an older adult population.