BACKGROUND: Overweight and asthma have increased during the last decades. Overweight is a known risk factor for asthma, but it is not known whether overweight may also increase asthma risk in the next generation. OBJECTIVE: We aimed to examine if parents overweight in childhood, adolescence or adulthood is associated with offspring asthma. METHODS: We included 6 347 adult offspring (age 18-52 yrs, investigated in the RHINESSA multigenerational study) of 2 044 fathers and 2 549 mothers (age 37-66 yrs, investigated in the ECRHS study). Associations of parental overweight at age eight, puberty and age 30, with offspring childhood overweight (potential mediator) and offspring asthma with or without nasal allergies (outcomes), was analyzed using two-level logistic regression and two-level multinomial logistic regression, respectively. Counterfactual-based mediation analysis was performed to establish whether observed associations were direct effects or indirect effects mediated through offspring's own overweight. RESULTS: We found statistical significant associations between both fathers' and mothers' childhood overweight and offspring's childhood overweight (odds ratio, OR 2.23; 95%CI 1.45, 3.42, and OR 2.45; 95%CI 1.86, 3.22, respectively). We also found a statistical significant effect of fathers' overweight onset in puberty on offspring asthma without nasal allergies (relative risk ratio RRR=2.31; 95% CI: 1.23, 4.33). This effect was direct and not mediated through offspring's own overweight. No effect on offspring asthma with nasal allergies was found. CONCLUSION: Our findings suggest that metabolic factors long before conception may increase asthma risk, and that male puberty is a time window of particular importance for offspring health.