The inability to synthesize information into experience of self and others could be one significant cause of negative symptoms. To explore this possibility, we examined the relationships between baseline metacognition and concurrent and prospective negative symptoms controlling for verbal memory. The participants were 62 adults diagnosed with serious mental illness enrolled in outpatient treatment. Metacognition was measured with the Metacognitive Assessment Scale–Abbreviated, symptoms were assessed using the Brief Psychiatric Rating Scale, and verbal memory was assessed using the California Verbal Learning Test. Significant correlations were found, indicating that poorer overall metacognition was associated with greater levels of negative symptoms assessed concurrently (r = 0.39) and 1 month later (r = 0.36). A significant relationship persisted after controlling for verbal memory and education. These findings support the idea that metacognitive deficits are related to negative symptoms and point to the potential of metacognitive interventions to positively influence negative symptoms.