Primary failure of eruption (PFE) is a rare non-syndromic condition involving total or partial non-eruption of posterior teeth, in the absence of mechanical obstruction. This paper presents the case of a healthy girl referred at age 4 years for asymmetry of upper arch. Clinical examination confirmed a slight shift of the upper midline to the left, with no erupted teeth distal to the upper left canine and left posterior open bite. Panoramic X-ray showed delayed intra-osseous development of lateral left upper teeth compared to the right side. Clinic and radiographic follow-up during the next 9 years showed that 26 has not erupted by almost 13 years of age, 27 has delayed development and an unusual shape and there is agenesis of 24, 25. Genetic analysis using the PTH1R single gene sequencing did not detect any known disease-causing or rare pathogenic variants that could explain the patient's phenotype. Even when detected early, PFE rises difficult problems with regard to diagnosis and ortho-surgical treatment planning due to the impossibility to accurately predict the evolution. Tooth agenesis on the same arch worsens the prognosis and adds challenges to planning the treatment. Close long-term follow-up and timely adjustment of treatment plan in accordance to the evolution of the case are needed.