BACKGROUND: We investigated the impact of multiple cardiovascular and neuropsychiatric diseases on all-cause and cause-specific mortality in older adults, considering their functional status. METHODS: This cohort study included 3241 participants (aged >= 60 years) in the Swedish National study of Aging and Care in Kungsholmen (SNAC-K). Number of cardiovascular and neuropsychiatric diseases was categorized as 0, 1, or >= 2. Functional impairment was defined as walking speed of < 0.8m/s. Death certificates provided information on 3- and 5-year mortality. Hazard ratios (HR) were derived from Cox models (all-cause mortality) and Fine-Gray competing risk models (cardiovascular and non-cardiovascular mortality). RESULTS: After 3 years, compared with participants with preserved walking speed and without either cardiovascular or neuropsychiatric diseases, the multivariable-adjusted HR (95% confidence interval) of allcause mortality for people with functional impairment in combination with 0, 1, and >= 2 cardiovascular diseases were 1.88 (1.29-2.74), 3.85 (2.60-5.70), and 5.18 (3.45-7.78), respectively. The corresponding figures for people with 0, 1, and >= 2 neuropsychiatric diseases were, respectively, 2.88 (2.03-4.08), 3.36 (2.314.89), and 3.68 (2.43-5.59). Among people with >= 2 cardiovascular or >= 2 neuropsychiatric diseases, those with functional impairment had an excess risk for 3-year all-cause mortality of 18/100 person-years and 17/100 person-years, respectively, than those without functional impairment. At 5 years, the association between the number of cardiovascular diseases and mortality resulted independent of functional impairment. CONCLUSIONS: Functional impairment magnifies the effect of cardiovascular and neuropsychiatric multimorbidity on mortality among older adults. Walking speed appears to be a simple clinical marker for the prognosis of these two patterns of multimorbidity.