This paper addresses the special problems in assessment of pupils who are congenitally or prelingually deafblind and who may have other disabilities, and argues that nonintrusive instruments and procedures are the assessment tools of choice. It contends that not enough attention has been given to developing, validating, and applying assessment procedures that meet the specialized needs of individuals whose major problem is not lack of inherent ability but a lack of opportunity to experience the world through the distance receptors of sound and/or sight, and that the use of inappropriate tests has led to placing children with deaf-blindness in unsuitable settings and cutting them off from learning what they must know for successful adaptation. The paper presents a fictitious case study to introduce nonintrusive assessment and BASIC (Behavioral Assessment Schedules for Individual Children), a nonintrusive assessment instrument. BASIC does not directly involve the pupil in a specific, structured task presented in a formal manner, but rather uses behavior observations. Ways in which nonintrusive assessments differ from currently applied standardized assessment tools are discussed, and nonintrusive measures that successfully assess persons who are deaf-blind are described. (CR)