Insulin restriction occurs when a person with diabetes takes less insulin than is prescribed and can occur for non-specified reasons (IR) or for specific reasons such as weight control (IRWC). This behavior has been associated with dangerous outcomes such as unhealthy elevations in blood glucose and mortality. IR may be particularly problematic during the transition from adolescence to emerging adulthood when other risky behaviors (e.g., disordered eating behaviors) and diabetes mismanagement commonly increase. Parental knowledge, disclosures to, and secrecy from parents are aspects of parental involvement that have been associated with increased risk behaviors and diabetes mismanagement in emerging adulthood. The present longitudinal study examined whether IR or IRWC increase from adolescence to emerging adulthood, and whether these aspects of parental involvement in diabetes may be predictors of insulin restriction during this time. Late adolescents who had been diagnosed with type 1 diabetes for longer than one year were recruited during their senior year of high school (N=236, 61% female; Mage=17.7 years) and surveyed annually for four years. IR and IRWC were measured with commonly used single items (e.g., “How often do you take less insulin than you should?”). Adolescent perceptions of parental knowledge about their diabetes self-care, as well as their diabetes-related disclosures to and secrecy from parents were measured separately for mothers and fathers. In contrast to expectations, unconditional growth curve models indicated IR declined across the four years while IRWC showed no linear change across time. Conditional models examining between-person effects revealed higher maternal knowledge, and lower secrecy from mothers and fathers at time 1 predicted lower IR at time 1, but also slower declines in IR across time. No between-person time 1 predictors were associated with IRWC intercept or slope. Time-varying covariate models revealed within-person fluctuations in parental involvement variables were associated with fluctuations in both IR and IRWC. In years when maternal knowledge and disclosure to fathers were higher than a person’s own average, and when secrecy to mothers and fathers were lower than a person’s average, IR was lower. Similarly, in years when disclosure to mothers was higher than a person’s own average and secrecy from fathers was lower than a person’s average, IRWC was lower. This research suggests that parental involvement in diabetes management remains important during early emerging adulthood and may represent a modifiable behavior to prevent or reduce IR.