The purposes of this study were to determine the clinical course of isolated congenital pseudarthrosis of the fibula (ICPF) and to establish optimal treatment guidelines for this disease. Thirteen fibulae in 12 patients with ICPF were followed for an average of 6.2 years. Twelve of the 13 fibulae were regarded to originally have had a pre-pseudarthrotic condition. Five fibulae remained intact during follow-up, but 8 developed pseudarthrosis. Two cases with established pseudarthrosis were observed for ankle alignment change without intervention, and in 4 cases successful fibular osteosynthesis maintained the ankle alignment. The remaining 2 adolescent cases presenting with ankle valgus were treated using the Ilizarov technique and distal tibiofibular synostosis. ICPF follows a unique clinical course, which should be taken into consideration along with fibular status, ankle alignment, and patient age when planning treatment.