This cross-sectional, convenience sampling study examined the relationship between diabetes-related factors, family functioning, and health-related quality of life (HRQOL) in 100 Turkish adolescents with type 1 diabetes mellitus (T1DM). The mean adolescent age was 14.65 ± 1.13 years. Quality of life was assessed using the Kiddo-KINDL generic HRQOL scale. Family functioning was assessed using the McMaster Family Assessment Device. The findings revealed that the participants had moderately high HRQOL. In terms of family functioning, "general family functions" subscale appeared healthy whereas "affective involvement" subscale appeared unhealthy. Results revealed that HbA1c was significantly negatively correlated with HRQOL. The full model of the socio-demographic, diabetes-related variables and general family functions to predict the total quality of life in children with T1DM was statistically significant. The overall multivariate model accounted for 58% of the variance of the total HRQOL. Regression analyses revealed that the levels of HbA1c and family functioning were significantly negatively related with HRQOL. The relationships between family functioning and HRQOL in adolescents with T1DM were unclear in Turkish sample. This research addressed this gap of knowledge, and provided a greater insight for practitioners working with adolescents with T1DM.