Objective To investigate the relationship between symptoms of post-traumatic stress disorder (PTSD) and the attachment patterns among parents who lost their only child. Methods A total of 149 individuals who lost their only child were randomly selected in an area of Shanghai, China. Post-traumatic stress disorder check list-civilian version (PCL-C) scale and adult attachment scale-revised edition (AAS-1996) were used to assess the symptoms of PTSD and adult attachment patterns. Results The prevalence rate of PTSD was 30.9% (46/149), and the prevalence rate of the females was significantly higher than that of the males (P<0.01). The prevalence rate of PTSD of the individuals with insecure attachment patterns was significantly higher than that of the individuals with secure attachment patterns (P<0.01), and the prevalence rates were significantly different between the two groups in the B (repeated traumatic experience), C (emotional numbness and avoidance) and D (increased alertness) of PTSD (all P<0.05). Different types of attachment patterns had different effects on PTSD, and the individuals with fear attachment patterns were more likely to develop PTSD. Conclusion The individuals losing their only child with insecure attachment patterns, especially the fear attachment patterns, are more likely to develop PTSD; and the prevalence rate of females losing their only child is significantly higher than that of males.