Autism spectrum disorder is associated with sensory processing alterations, such as sensory hyper- and hypo-responsiveness. Twin studies are scarce in this field, but they are necessary in order to disentangle the genetic and environmental contributions to this association. Furthermore, it is unclear how different neurodevelopmental/psychiatric conditions contribute to altering sensory processing. We investigated the association between autistic traits/autism spectrum disorder diagnosis and sensory processing alterations in twins (N = 269), using the adult/adolescent sensory profile, which differentiates four sub-domains: Low Registration, Sensation Seeking, Sensory Sensitivity, and Sensation Avoiding. While the associations between autistic traits and "Low Registration" and "Sensation Avoiding" persisted within monozygotic (genetically identical) twins, "Sensory Sensitivity" was only associated with autistic traits within dizygotic twins. In multivariate analyses with different neurodevelopmental/psychiatric diagnoses as predictor variables, autism spectrum disorder and attention deficit hyperactivity disorder were the strongest predictors for two adult/adolescent sensory profile sub-domains each. The results suggest that the association between autistic traits and "Sensory Sensitivity" is influenced by genetics while non-shared environmental factors influence the associations between autistic traits and "Low Registration" and "Sensation Avoiding." They further indicate that altered sensory processing is not specific to autism spectrum disorder, while autism spectrum disorder is a strong predictor of certain sensory processing alterations, even when controlling for other (comorbid) neurodevelopmental/psychiatric conditions.