Discoid meniscus is a well-known meniscal dysmorphia affecting more often the lateral meniscus of the knee. Familial series are exceptional with only two reported instances. A new series of three bilateral symptomatic cases of lateral discoid menisci was reported in a family of three brothers and sisters, whom parents had never suffered from their knees. During operative procedure four complete and two incomplete types were found. Two complete and four partial meniscectomies have been performed followed by four good results in the five with sufficient follow-up. The origin of this malformation is unknown. The phylogenetic and ontogenetic studies give no explanation and genetic factors seem to have a minor role.