Emotional self-awareness is increasingly suggested to be an area of difficulty in autism that may predict socioemotional outcomes for this population. However, whether emotional self-awareness is consistently diminished in autism across age and methodology remains unclear. We systematically reviewed 47 papers measuring emotional self-awareness in autistic (n=1387) and non-autistic (n=1433) participants. Most studies relied on self-report. Of studies testing for group differences, the majority (32/41) found significantly poorer emotional self-awareness in autism. Meta-analyses of self-report measures found that emotional self-awareness was significantly poorer in autism (d=1.16). However, when examining age groups individually, autistic children of age 12 years and under were not significantly different from their peers (d=0.03). Instead, difficulties emerged during adolescence (d=0.63) and increased with age (d=1.16-1.58). The pattern of emotional self-awareness difficulties being more common in autism, and worsening with age is similar to the development of mental health difficulties in autism. However, findings rely on self-perception and so may reflect poor self-beliefs of socioemotional competence. We propose that negative self-beliefs in autistic populations may account for findings of low emotional self-awareness.