Achilles tendinitis and tenosynovitis may be an early manifestation of familial type II hyperlipoproteinemia in the pediatric and adolescent age groups, as evidenced by the five kindreds in this report. Episodes of arthritic symptoms usually antedated the appearance of palpable extensor-tendon xanthomas, were gradual in onset, lasted for two or three days, involved one or both Achilles tendons, and resolved spontaneously within 48 to 72 hours. The tendons were often warm, erythematous, and extremely painful to palpation. Appropriate recognition of this diagnostic clinical finding offers the opportunity for early therapy with diet or cholestyramine resin, with an aim toward prevention of premature atherosclerosis in adulthood.Acute tendinitis or tenosynovitis -Zi. in children may herald a number of disorders, including gonococcal ar-