Background Knowledge on factors related to preventable medication waste and waste-reducing interventions, including redispensing unused medications, is needed to maximise effectiveness. Objective To assess patient and medication factors associated with preventable medication waste and possibilities for redispensing unused medications. Setting Dutch community pharmacies. Methods In this cross-sectional study, pharmacy-staff registered patient and medication characteristics of prescription medications returned to 41 Dutch community pharmacies during 1 week in 2014. Medications were classified as preventable waste if the remaining amount could have been prevented and as theoretically eligible for redispensing if the package was unopened, undamaged and ≥ 6 months until the expiry date. Associations were analysed using multivariate logistic regression. Main outcome measures Proportion of medications classified as preventable waste and as eligible for redispensing, including factors associated with these medications. Results Overall, 279 persons returned 759 (low-cost) medications, and 39.3% was classified as preventable waste. These medications were more frequently used by men than women (OR; 1.7[1.2-2.3]) and by older (> 65 years) than younger patients (OR; 1.4[1.0-2.0]). Medications dispensed for longer periods were more often unnecessary wasted (1-3 months OR; 1.8[1.1-3.0], > 3 months 3.2[1.5-6.9]). Of all returned medications, 19.1% was eligible for redispensing. These medications were more frequently used by men than women (OR; 1.9[1.3-2.9]). Medications chronically used were more frequently eligible for redispensing than acute use (OR; 2.1[1.0-4.3]), and used for longer periods (1-3 months OR; 4.6[2.3-8.9], > 3 months 7.8[3.3-18.5]). Conclusions Over one-third of waste due to medications returned to community pharmacies can be prevented. One-fifth of returned medications can be redispensed, but this seems less interesting from an economic viewpoint.