Severe combined immunodeficiency (SCID) can be caused by deleterious mutations in DCLRE1C, leading to deficient non-homologous end joining by compromising the function of the Artemis protein. This impairs the process of V(D)J recombination of the T- and B-cell receptors and typically results in radiosensitive T-, B-, NK+ SCID presenting during the first months of life. We present a case of a 3-year-old girl with two novel compound heterozygous variants in DCLRE1C (c.58G>C and c.374A>C) that were associated with marked reduced numbers of peripheral T- and B-cells and undetectable total serum IgG. Despite the severe laboratory phenotype, the patient had a normal development, albeit failure to thrive (-2.5 to -3 SD), during her first years of life including day-care attendance at preschool for 1.5 years. After being diagnosed with pneumonia the clinical picture of SCID was recognized and the girl successfully underwent hematopoietic stem-cell transplantation.