Compassion is known to predict prosocial behavior and moral judgments related to harm. Despite the centrality of compassion to social life, factors predicting adulthood compassion are largely unknown. We examined whether qualities of parent-child-relationship, namely, emotional warmth and acceptance, predict offspring compassion decades later in adulthood. We used data from the prospective population-based Young Finns Study. Our sample included 2,761 participants (55.5% women). Parent-child-relationship qualities were reported by each participant's parents at baseline in 1980 (T0) when participants were between 3 and 18 years old. Compassion was self-reported 3 times: in 1997 (T1), 2001 (T2), and 2012 (T3) with the Temperament and Character Inventory (Cloninger, Przybeck, Svrakic, & Wetzel, 1994). By using age at the assessment as a time-variant variable, we applied multilevel modeling for repeated measurements to examine developmental trajectories of compassion from the ages of 20 (the age of the youngest cohort at T1) to 50 (the age of the oldest cohort at T3). On average, compassion increased in a curvilinear pattern with age. Higher acceptance (p = 0.013) and higher emotional warmth (p < 0.001) were related to higher compassion in adulthood. After adjusting for childhood confounds (i.e., participant gender, birth cohort, externalizing behavior, parental socioeconomic status, and parental mental health problems), only emotional warmth (p < 0.001) remained a significant predictor of compassion. Quality of the parent-child-relationship has long-term effects on offspring compassion. An emotionally warm and close relationship, in particular, may contribute to higher offspring compassion in adulthood.