This is a report on arthroscopic treatment of an abnormal femoral origin of the anterior cruciate ligament (ACL) in combination with a discoid lateral meniscus in a 3-year-old child. The discoid lateral meniscus was treated by resection of the inner part with punches and by use of the holmium:YAG laser. The abnormal femoral origin of the ACL which was found inserting over the whole length of the intercondylar notch in anterior-posterior direction was detached at the anterior part with the laser. At examination after 1 year, the child was completely pain-free without any instability of the knee. A magnetic resonance image showed a normal ACL and a normal lateral meniscus in the operated knee.