Background: The leading cause of death in older people is cardiovascular diseases. Several studies have found that neck circumference (NC) is a simple anthropometric marker associated with adiposity. The aim of this study is to estimate and validate NC cut-off points as adiposity markers and analyze their association with cardiovascular and chronic metabolic diseases in older people. Methods: A cross-sectional study in 358 non-disabled, community-dwelling older people (71.7 ± 3.9 years) living in Santiago de Chile and participating in the HTSMayor study was conducted. Measurements of body composition and cardiovascular risks were evaluated. Receiver operating characteristic (ROC) curves and multiple logistic regression models were used to evaluate the association of NC with cardiovascular and chronic metabolic diseases. NC cut-off points were obtained to predict obesity, abdominal obesity, and adiposity. Results: The best performance values of neck circumference relative to obesity and adiposity were obtained with respect to abdominal obesity (40.6 cm in men and 34.2 cm in women). Higher NC values were associated with a higher area under the curve (AUC) for men and women (men: AUC = 0.84; women: AUC = 0.86). NC was significantly associated with a higher risk for diabetes mellitus (OR = 1.95), hypertension (OR = 2.42), acute myocardial infarction (OR = 4.36), and comorbidities (OR = 2.01), and a lower risk for sarcopenia (OR = 0.35). Conclusions: This study shows that NC is a useful tool for detecting abdominal obesity, obesity, and adiposity in older people and that a higher NC increases the risk of chronic diseases.