Need is a multi-faceted, multi-dimensional concept. National and international efforts to assess the needs of the elderly confront common problems: lack of an accepted definition of terms such as "needs," "want" and "demand;" perceptions which vary with age, professional role, relationship and time; a range of methodologies encompassing rational, empirical and relativistic approaches, as well as subjective, objective and statistical measures. Research instruments are being refined and shared, but the state of the art remains in its infancy. Use of index of incapacity measures appears to offer the best data base for planning needed services.