Objectives: To establish the course of metabolic syndrome (MS) rates in older patients with severe mental illness (SMI) after 5-year follow-up and evaluate whether MS at baseline is associated with mortality or diabetes at follow-up. Methods: Patients (>60 years of age) with SMI (N = 100) were included at a specialized mental health outpatient clinic. Metabolic parameters were collected from patients' medical files at baseline and after 5-year follow-up. Results: Follow-up data were available of 98 patients (98%); nine patients had died. Parameters of MS were available of 76 patients; 34.2% were diagnosed with MS. This was not significantly different compared with baseline (46.1%). MS at baseline was not significantly associated with mortality or development of diabetes at follow-up. Conclusions: In older patients with SMI, the rates of MS may reach a plateau. Screening for MS in older patients treated at a specialized mental health outpatient clinic may generate attention for their somatic health and treatment for the components of MS that may in turn have a positive effect on their outcome. However, further research with larger sample sizes is needed in order to confirm these findings.