Medical devices classified here—such as surgical instruments (9018), orthopedic implants (9021), and diagnostic radiation equipment (9022)—must comply with FDA device regulations, which require the device to be listed with FDA and the establishment to be registered. Depending on the device's risk classification, premarket notification (510(k)) or premarket approval (PMA) may be required before the device can be legally marketed or imported for commercial sale.

Chapter 90 covers instruments and apparatus whose primary function is measuring, checking, analyzing, or controlling a physical or chemical property. If the article's principal function is electrical power conversion, signal transmission, or data processing rather than measurement, it is more likely classified in the electrical machinery chapter. The chapter notes and the 'principal function' test in the General Rules of Interpretation guide the boundary determination.

Heading 9013 covers lasers other than laser diodes, along with other optical appliances and instruments not more specifically described elsewhere in Chapter 90. Laser diodes are semiconductor devices classified under the electrical machinery chapter. A laser incorporated as a functional component of a machine tool for material removal may instead be classified with that machine tool under the machinery chapter, depending on how the complete article is presented.