Osteopetrosis is a rare genetic disorder caused by osteoclast failure. Dominant negative mutations of the ClCN7 gene cause the so-called, autosomal dominant osteopetrosis type II, which represents the most frequent and heterogeneous form of osteopetrosis, ranging from asymptomatic to intermediate-severe, thus suggesting additional genetic and environmental determinants affecting penetrance. Here, we present a case a 46 year-old woman complained low back pain for 15 years. The patient lacked any history of direct trauma and her pain was radiating to her left leg, increasing with physical activity, she had no pain at nights. The patient was diagnosed with autosomal dominant osteopetrosis on the basis of the presence of typical radiological appearance. Were present a case report of osteopetrosis type II (an autosomal dominantly inherited disease) as a cause for low back pain without any familial penetrance of the disease.