Background The number of individuals who experience the onset of attention-deficit/hyperactivity disorder (ADHD)-like symptoms after the age of 12 years has been growing, which does not meet the diagnostic criteria for adult ADHD. We designated this condition as "pseudo-ADHD" and investigated its psychological implications by comparing the parenting attitudes in childhood and attachment styles among individuals with "pseudo-ADHD," those with adult ADHD, and healthy controls. Methods We conducted an online cross-sectional survey of adults aged 18 years. Participants in the analysis included individuals with "pseudo-ADHD" (n = 46), adults with ADHD (n = 23), and healthy controls (n = 758). The Parental Bonding Instrument (PBI) was used to evaluate parenting attitudes, and the Experiences in Close Relationships Inventory for the Generalized Other (ECR-GO) was used to evaluate attachment styles. One-way analysis of variance was performed to compare the PBI and ECR-GO scores among the three groups. Results Regarding the PBI scores, a significant main effect of group was found for the paternal care scores (p = 0.002), and the "pseudo-ADHD" group did not differ significantly from the adult ADHD group or healthy control group (p = 0.378, p = 0.228, respectively). A significant main effect of the group was found for the maternal care scores (p < 0.001). The "pseudo-ADHD" group scored significantly lower than the adult ADHD group (p = 0.005), whereas there was no significant difference compared to the healthy control group (p = 1.000). A significant main effect of the group was also found for the paternal overprotection scores (p < 0.001). The "pseudo-ADHD" group scored significantly lower than the adult ADHD group (p = 0.002), whereas there was no significant difference compared to the healthy control group (p = 0.571). A significant main effect of group was found for the maternal overprotection scores (p < 0.001), and the "pseudo-ADHD" group did not differ significantly from either the adult ADHD group or the healthy control group (p = 0.060, p = 0.161, respectively). Regarding ECR-GO scores, a significant main effect of group was found for the fear of abandonment score (p < 0.001), and the "pseudo-ADHD" group scored significantly lower than the adult ADHD group (p < 0.001) and significantly higher than the healthy control group (p = 0.005). Conclusion This study suggested that the parenting attitudes of parents of individuals with "pseudo-ADHD" were not different from those of the healthy controls. For attachment styles, the fear of abandonment was higher in individuals with "pseudo-ADHD" than in healthy controls, but not as high as in patients with adult ADHD. This study highlights, for the first time, the importance of considering attachment styles in the diagnosis and treatment of individuals with ADHD symptoms in adulthood.