Hypomineralized primary second molars (HPSM) are characterized by enamel opacities accompanied by hypersensitivity and atypical caries lesion, on one to four primary second molars. The correct treatment and follow-ups of those teeth have an important impact on a correct eruption of the first permanent molars and future occlusion. Hence, this report aims to describes a case of a severe HPSM in all second molars of a four-year-old girl and subsequent four-year follow-ups. The rehabilitation involved the placement of four stainless steel crowns on all four second primary molars under general anesthesia. Concerning the available literature and the case severity of HPSM, the treatment approach proposed for the case provided good functional outcome.