Deleting a series will also delete all items in history for that series.

NzbDrone.Core/Providers/SeriesProvider.cs

@@ -128,6 +128,10 @@ namespace NzbDrone.Core.Providers
                 //Delete Files, Episdes, Seasons then the Series
                 //Can't use providers because episode provider needs series provider - Cyclic Dependency Injection, this will work
 
+                Logger.Debug("Deleting History Items from DB for Series: {0}", series.SeriesId);
+                var episodes = series.Episodes.Select(e => e.EpisodeId).ToList();
+                episodes.ForEach(e => _repository.DeleteMany<History>(h => h.EpisodeId == e));
+
                 Logger.Debug("Deleting EpisodeFiles from DB for Series: {0}", series.SeriesId);
                 _repository.DeleteMany(series.EpisodeFiles);