IDD is the acronym for intellectual and developmental disabilities, written without a slash. It names the same service population as I/DD. The missing punctuation is a style choice you will see in office names, report titles, and statutes. It is not a different condition and it is not a narrower eligibility category.
State agencies use it in their own names. So do national projects. National Core Indicators publishes an IDD survey of people receiving these services, separate from its survey of older adults and people with physical disabilities. A chart labeled NCI-IDD is about this system. A chart labeled only IDD might be a state department. Read the noun next to the letters before assuming a waiver, an agency, or a dataset.
The acronym shows up in job ads ("IDD experience preferred") as a shorthand for having worked in these services. It does not specify whether the work was direct support, coordination, nursing, or administration. It also does not say which developmental disability the employer means. Agencies use it because the full paired phrase is long, and because their funding stream is already called IDD.
Nothing about the acronym is a clinical finding. It will not tell you how a disability was identified, and it should not be read as a diagnosis written in capital letters. Programs that say IDD still enroll people through a level-of-care decision. The letters on the door are the name of the office.
If a document uses IDD and a family uses I/DD, they are not disagreeing. If a document uses IDD and means only intellectual disability, it has dropped a word. Look for the expansion on first reference. This desk expands it.
Pages and statutes that use the acronym are about this service system. They are not a separate medical specialty. If the expansion is missing, expand it to intellectual and developmental disabilities. If the writer clearly meant only one of those words, use that entry instead.