Background Childhood maltreatment (CM) is strongly associated with psychiatric disorders in childhood and adulthood. Previous findings suggest that the association between CM and psychiatric disorders is partly causal and partly due to familial confounding, but few studies have investigated the mechanisms behind the association between CM and neurodevelopmental disorders (NDDs). Our objective was to determine whether maltreated children have an elevated number of NDDs and whether CM is a risk factor for an increased NDD ‘load’ and increased NDD symptoms when controlling for familial effects. Methods We used a cross‐sectional sample from a population‐representative Swedish twin study, comprising 8,192 nine‐year‐old twins born in Sweden between 1997 and 2005. CM was defined as parent‐reported exposure to emotional abuse/neglect, physical neglect, physical abuse, and/or sexual abuse. Four NDDs were measured with the Autism–Tics, AD/HD, and other comorbidities inventory. Results Maltreated children had a greater mean number of NDDs than nonmaltreated children. In a co‐twin control design, CM‐discordant monozygotic twins did not differ significantly for their number of NDDs, suggesting that CM is not associated with an increased load of NDDs when genetic and shared environmental factors are taken into account. However, CM was associated with a small increase in symptoms of attention‐deficit/hyperactivity disorder and autism spectrum disorder in CM‐discordant MZ twins, although most of the covariance of CM with NDD symptoms was explained by common genetic effects. Conclusions Maltreated children are at higher risk of having multiple NDDs. Our findings are, however, not consistent with the notion that CM causes the increased NDD load in maltreated children. Maltreated children should receive a full neurodevelopmental assessment, and clinicians should be aware that children with multiple NDDs are at higher risk of maltreatment.