Over the past years, diffusion tensor imaging (DTI) has become an important brain-imaging technique in neuropsychiatric research. DTI allows noninvasive visualization of white matter tracts. In addition, with DTI it is possible to quantify the structural integrity of the investigated fiber tracts. In child and adolescent psychiatry, DTI has become an increasingly important research tool, especially for conditions like autism spectrum disorders (ASD). Yet, correct interpretation of DTI findings can be challenging, especially for clinicians. Thus, the present review article explains the basic principles of this frequently used imaging technique as well as essential indices, like fractional anisotropy, radial, mean, and axial diffusivity and its two main applications, fibertracking and whole brain analysis. The strengths and weaknesses as well as future perspectives are discussed in light of DTI studies in children and adolescents with ASD.