A narrow window of bone age (BA) in slipped capital femoral epiphysis (SCFE) was described a decade ago. Children now mature younger. Does the BA narrow window still exist? It is the purpose of this study to investigate this question. A retrospective review of children with idiopathic SCFE (1998-2003) was performed. The initial study data ("past") were used as a comparison. Anteroposterior pelvis radiographs were scored for BA (Oxford method) in 108 children. Only the first radiograph was used for children with sequential bilateral SCFEs. There were 67 boys and 41 girls. There were 73 children with unilateral and 35 with bilateral SCFEs. Chronological age (CA) was 12.4 ± 1.8 years; Oxford score, 39 ± 3 years; and Oxford BA (OXBA), 13.2 ± 1.3 years. The recent children were younger (12.1 and 13.2 years; P = 0.001), with lower OXBA (29.0 and 31.4; P = 0.000003). When converted into years, there was no significant difference between the recent and past children (recent data, 13.1 years; past data, 13.5 years; P = 0.18). Chronological age was higher in boys than in girls (12.7 and 11.6 years, respectively; P = 0.0008), and so was BA (13.9 ± 1.0 and 12.0 years, respectively; P < 10−6). There were no differences in BA score between boys and girls (boys, 29.5; girls, 29.9; P = 0.49). The recent data demonstrated the same narrow window of BA. The CA range for the boys' SCFE was 8.4 years, whereas the OXBA was 4.0 years. The CA range for girls was 5.3 years, whereas the OXBA was 2.3 years. Those with unilateral SCFEs were older than those with bilateral SCFEs in CA (12.7 and 11.7 years, respectively; P = 0.013), but not in BA (29.8 and 29.4; P = 0.51). All SCFEs are present, on average, at an OXBA of 29, regardless of sex, symptom duration, or unilateral/bilateral nature. This study has reaffirmed the narrow window of BA in SCFE, with a BA range approximating 50% of CA range.