diff --git a/database/application.go b/database/application.go
index 213ef7b..3f001a8 100644
--- a/database/application.go
+++ b/database/application.go
@@ -31,6 +31,7 @@ func (d *GormDatabase) CreateApplication(application *model.Application) error {
 
 // DeleteApplicationByID deletes an application by its id.
 func (d *GormDatabase) DeleteApplicationByID(id uint) error {
+	d.DeleteMessagesByApplication(id)
 	return d.DB.Where("id = ?", id).Delete(&model.Application{}).Error
 }
 
diff --git a/database/application_test.go b/database/application_test.go
index b25cfcb..7a72d7b 100644
--- a/database/application_test.go
+++ b/database/application_test.go
@@ -42,3 +42,21 @@ func (s *DatabaseSuite) TestApplication() {
 
 	assert.Nil(s.T(), s.db.GetApplicationByID(app.ID))
 }
+
+func (s *DatabaseSuite) TestDeleteAppDeletesMessages() {
+	s.db.CreateApplication(&model.Application{ID: 55, Token: "token"})
+	s.db.CreateApplication(&model.Application{ID: 66, Token: "token2"})
+	s.db.CreateMessage(&model.Message{ID: 12, ApplicationID: 55})
+	s.db.CreateMessage(&model.Message{ID: 13, ApplicationID: 66})
+	s.db.CreateMessage(&model.Message{ID: 14, ApplicationID: 55})
+	s.db.CreateMessage(&model.Message{ID: 15, ApplicationID: 55})
+
+	s.db.DeleteApplicationByID(55)
+
+	assert.Nil(s.T(), s.db.GetMessageByID(12))
+	assert.NotNil(s.T(), s.db.GetMessageByID(13))
+	assert.Nil(s.T(), s.db.GetMessageByID(14))
+	assert.Nil(s.T(), s.db.GetMessageByID(15))
+	assert.Empty(s.T(), s.db.GetMessagesByApplication(55))
+	assert.NotEmpty(s.T(), s.db.GetMessagesByApplication(66))
+}
diff --git a/database/user.go b/database/user.go
index abc966f..d14271b 100644
--- a/database/user.go
+++ b/database/user.go
@@ -33,6 +33,12 @@ func (d *GormDatabase) GetUsers() []*model.User {
 
 // DeleteUserByID deletes a user by its id.
 func (d *GormDatabase) DeleteUserByID(id uint) error {
+	for _, app := range d.GetApplicationsByUser(id) {
+		d.DeleteApplicationByID(app.ID)
+	}
+	for _, client := range d.GetClientsByUser(id) {
+		d.DeleteClientByID(client.ID)
+	}
 	return d.DB.Where("id = ?", id).Delete(&model.User{}).Error
 }
 
diff --git a/database/user_test.go b/database/user_test.go
index a6a483a..d40437f 100644
--- a/database/user_test.go
+++ b/database/user_test.go
@@ -45,3 +45,33 @@ func (s *DatabaseSuite) TestUser() {
 	users = s.db.GetUsers()
 	assert.Empty(s.T(), users)
 }
+
+func (s *DatabaseSuite) TestDeleteUserDeletesApplicationsAndClients() {
+	s.db.CreateUser(&model.User{Name: "nicories", ID: 10})
+	s.db.CreateApplication(&model.Application{ID: 100, Token: "apptoken", UserID: 10})
+	s.db.CreateMessage(&model.Message{ID: 1000, ApplicationID: 100})
+	s.db.CreateClient(&model.Client{ID: 10000, Token: "clienttoken", UserID: 10})
+
+	s.db.CreateUser(&model.User{Name: "nicories2", ID: 20})
+	s.db.CreateApplication(&model.Application{ID: 200, Token: "apptoken2", UserID: 20})
+	s.db.CreateMessage(&model.Message{ID: 2000, ApplicationID: 200})
+	s.db.CreateClient(&model.Client{ID: 20000, Token: "clienttoken2", UserID: 20})
+
+	s.db.DeleteUserByID(10)
+
+	assert.Nil(s.T(), s.db.GetApplicationByToken("apptoken"))
+	assert.Nil(s.T(), s.db.GetClientByToken("clienttoken"))
+	assert.Empty(s.T(), s.db.GetClientsByUser(10))
+	assert.Empty(s.T(), s.db.GetApplicationsByUser(10))
+	assert.Empty(s.T(), s.db.GetMessagesByApplication(100))
+	assert.Empty(s.T(), s.db.GetMessagesByUser(10))
+	assert.Nil(s.T(), s.db.GetMessageByID(1000))
+
+	assert.NotNil(s.T(), s.db.GetApplicationByToken("apptoken2"))
+	assert.NotNil(s.T(), s.db.GetClientByToken("clienttoken2"))
+	assert.NotEmpty(s.T(), s.db.GetClientsByUser(20))
+	assert.NotEmpty(s.T(), s.db.GetApplicationsByUser(20))
+	assert.NotEmpty(s.T(), s.db.GetMessagesByApplication(200))
+	assert.NotEmpty(s.T(), s.db.GetMessagesByUser(20))
+	assert.NotNil(s.T(), s.db.GetMessageByID(2000))
+}