Nearly all autistic youth have special interests (SIs), which are associated with many benefits and challenges. Most research on SIs has focused on the subject matter of SIs, with less focus on understanding how youth engage in their SIs. We conducted a qualitative study using inductive content analysis (ICA) to examine: (1) The modalities youth use to engage in their SIs, (2) the degree to which such modalities are described by caregivers as adaptive or maladaptive, and (3) the extent to which the SIs themselves are described by caregivers positively or negatively. We coded responses from 1922 caregivers of autistic youths who completed an online version of the Special Interests Survey, a caregiver-report measure of SIs. Responses to open-ended questions on the SIS, wherein caregivers describe the specific interest within the endorsed SI category, were used as data for the ICA. Frequencies of the codes were derived from cross-tabulation data. The ICA yielded eight modalities: perseverating, creating, information-seeking, memorizing, collecting, attachment, sensory-seeking, and self-soothing. Perseverating, collecting, and attachment were described as maladaptive and negatively by caregivers, whereas creating and information-seeking were described as adaptive. SIs with the greatest proportion of positive and negative descriptions were Plants and Objects, respectively. These findings suggest that SIs - and the degree to which they are described as beneficial or problematic - may be associated with modality and the subject matter. Considering how autistic individuals engage in SIs has implications for clinical work and future research in this area.