BACKGROUND: Previous reports of ultrasonographically diagnosed seizure activity in utero have described fetuses with obvious, gross, tonic-clonic movements of trunk and extremities. CASES: Three fetuses with akinesia deformation sequence are described: two with arthrogryposis multiplex congenita and one with Pena-Shokeir syndrome. Each was demonstrated by serial real-time ultrasound examinations to have joint contractures, absent fetal breathing motions, and lack of gross movements other than sonographically evident subtle seizure activity. CONCLUSION: Fetal seizure activity can be subtle when seen in the presence of fetal anomalies that limit joint movement. The prognosis remains poor.