Phalangeal cone-shaped epiphyses are an ideal object for the radiologist to study with temporal reasoning, to examine their shape, diagnostic usefulness, natural history and effect on pathophysiology. Radiographs of the hands of 60 patients with cartilage hair hypoplasia (CHH), 69 with trichorhinophalangeal syndrome I (TRP I) and 11 with TRP II were examined, including 26 longitudinal observations. The early phases of cone development were recorded. In CHH a characteristic mesophalangeal type of cone in 42/47 patients of the "Age Suitable for Classification" (ASC) was detected. All 46 TRP I and 9 TRP II patients in the ASC had the previously described mesophalangeal cone type 12. However, 1/4 of these TRP I and all TRP II cases presented a milder variant of type 12: type 12 A. A complex sequence of secondary changes in the proximal interphalangeal joints in TRP I leading eventually to subluxation was recorded. It can be concluded that in the ASC the cones described are highly sensitive but not specific diagnostic indicators. In infancy and early childhood, other phalangeal changes were found, which may be of diagnostic help.